Preterm Labor Evaluation

Preterm labor is defined as regular uterine contractions in conjunction with cervical dilation and/or effacement (25). Multiple risk factors for preterm labor include nonwhite race, age less than 17 or more than 35 years old, low socioeconomic status, low prepregnancy weight, history of preterm birth, vaginal bleeding during pregnancy, and smoking (26). The pathophysiology of preterm labor relates to activation of the labor process that is similar, but prior, to a term gestation. There is a physiologic activation of the “common labor pathway,” with anatomical, biochemical, immunologic, and endocrinologic events that dilate the cervix, rupture amniotic membranes, and cause uterine contractions to evacuate the fetus. The preterm activation of this “common labor pathway” is considered pathologic and may relate to a multitude of diseases to include underlying uterine infections, systemic infections and microbial induced inflammation, uterine distention, placental dehiscence, and even maternal stress (27). Both surgical syndromes and trauma may induce the activation of preterm labor, making it critical to recognize and employ treatment when appropriate. Preterm labor is frequent among surgical interventions. In one series of 77 patients undergoing nonobstetric surgery, preterm labor was seen in 26% of patients in the second trimester and in 82% of those in the third trimester. Preterm labor leading to preterm delivery was most common after appendicitis and adnexal surgery, where preterm birth was seen in 16% of the patients. However, only 5% of surgical cases demonstrated a clear established link to the surgical procedure (10). Another study showed 18% of 62 pregnant subjects with nonobstetric abdominal surgery delivered preterm, again associating abdominal surgery to preterm birth (28).

The evaluation of preterm labor may include imaging and laboratories in addition to the history and physical examination. Fetal monitoring should begin to assess the frequency of patient perceived and nonperceived contractions and to evaluate fetal status by the fetal heart rate pattern. In general, patients with pregnancies beyond 34 wGA are monitored for contractions and cervical change, evaluated for rupture of membranes (ROM) and urinary tract infections, hydrated, and if the fetal heart rate is reactive (reassuring), then the patient is expectantly managed in an observed environment. A re-examination will determine the presence of preterm labor and for appropriate disposition (25). For those patients between 24 and 34 wGA, additional diagnostic modalities may include an ultrasound for cervical length, fetal fibronectin screen (FFN), vaginitis swab, and culture for Gonorrhea or Chlamydia for those at risk for the disease (25,29). The cervical length is performed by an intravaginal ultrasound that measures the external os distance from the internal os and presenting fetal part in the lower uterine segment over a 5-minute period. Cervical lengths of more than 3 cm indicate a low likelihood of preterm labor, while lengths of 1.5 to 3 cm require further diagnostic intervention or monitoring, usually in conjunction with FFN. Lengths less than 1.5 cm have a high incidence of preterm labor. The detection of the biomarker fetal fibronectin in the vaginal vault can be used independently or in conjunction with cervical length screening, and if negative, carries a 98% negative predictive value (NPV) for subsequent delivery in the next 7 days and rules against preterm labor (30). FFN has a poor positive predictive value (PPV), so if the test is positive, further diagnostic workup should ensue. A limited abdominal ultrasound (US) documenting fetal number and position, amniotic fluid (maximum vertical pocket or amniotic fluid index), and location and characterization of the placenta is performed. The underlying cause of preterm labor should be aggressively sought after and treated, especially in cases of acute abdomen and/or trauma.

Evaluating if the patient has ROM is paramount in every preterm labor evaluation. In addition to the patient history, this can be diagnosed by a sterile speculum examination and visualization of pooling amniotic fluid from the cervix, or in the use of adjuvant laboratories evaluating for alkaline fluid in the vagina (i.e., Nitrazine), biomarker detection of amniotic fluid containing PAMG-1 (i.e., AmniSure) (31), or the presence of ferning on a microscopic slide. The gold standard detection of ruptured membranes in equivocal cases is the tampon dye test, involving an infusion of inert dye (at the time of amniocentesis) into the uterine cavity and evaluating a vaginally placed tampon for colored dye 1 hour after. In the event of membrane rupture, the diagnosis of preterm premature ROM indicates immediate hospital admission and specific management protocols as these patients have higher risks of labor, placental abruption, and intrauterine infection (32).

Preterm Labor Management

Patients with preterm labor after 34 wGA usually are managed expectantly, that is, without attempts to stop the labor process. In most patients between 24 and 34 wGA, there is indication for antenatal corticosteroid administration for neonatal benefit to reduce neonatal acute respiratory distress, necrotizing enterocolitis, intraventricular hemorrhage, and other disabling neonatal diseases (33,34). Two common regimens include either two doses of intramuscular betamethasone 12 mg given 24 hours apart or four doses of intramuscular dexamethasone 6 mg 6 hours apart (34). To quell the uterine contractions for the full administration and effect of corticosteroid administration, it is common to utilize a tocolytic regimen such as indomethacin PO, nifedipine i.v. or PO, or magnesium sulfate i.v. drip for approximately 48 hours. The choice of drug is determined by the maternal condition and gestational age. Contraindications to tocolytic medications include intrauterine fetal demise, lethal fetal anomalies, nonreassuring fetal status, severe preeclampsia or eclampsia, maternal bleeding and hemodynamic instability, preterm premature ROM (in most cases), and maternal intolerance of the tocolytic (25). Finally, there is recent evidence that administration of magnesium sulfate i.v. drip within hours of delivery for neonates less than 32 wGA can reduce cerebral palsy in the survivors, commonly termed as “magnesium for fetal neuroprotection” (35).

Consultants

The recognition, management, and treatment of preterm labor or preterm premature ROM should be in conjunction with an obstetrician and neonatology/pediatric consultation at a hospital that provides such services. These consultants will be able to provide consultation on the labor and postpartum course for the mother and fetus and help the general surgeon or intensivist with specifics of management. In the event of a surgical procedure, ACOG has stated, “it is important for a physician to obtain an obstetric consultation before performing nonobstetric surgery and some invasive procedures (e.g., cardiac catheterization or colonoscopy) because obstetricians are uniquely qualified to discuss aspects of maternal physiology and anatomy that may affect intraoperative maternal–fetal well-being” (3). In addition, the obstetrician may provide information to help distinguish the acute abdomen from pregnancy related conditions and give recommendations on timing and route of delivery, appropriate medication and diagnostic imaging usage in pregnancy, and updates on fetal status. The neonatologist consultant works closely with the obstetrician to provide continued care for the neonate after delivery, educate families regarding neonatal aspects of care, and whether to perform a cesarean section and/or neonatal resuscitation on an individualized basis. Although the overall prognosis for premature infants has steadily improved, the morbidity and mortality for extremely low–birth-weight infants remains high. The mean survival rates for infants born between 23 and 25 wGA increase from 30%, to 52%, to 76% with each additional week of development. Likewise, the survival for infants weighing 401 to 800 g ranges from 11% in those under 500 g to 74% in those over 701 g. Severe disability is common among survivors in this group of vulnerable neonates and noninitiation of resuscitation for newborns under 23 wGA or 400 g birth weight is appropriate (36).

Ultrasound

Obstetric US serves to assess fetal number, viability, size, gestational age, position, anatomy, as well as amniotic fluid volume, uterine mapping, and placental location and characterization (38). Obstetric US studies can be limited to evaluate basic pregnancy information or provide comprehensive information on detailed anatomy or even fetal echocardiography.

In the trauma setting, surgeon-performed focused assessment with sonography for trauma (FAST) is a useful screening tool for intra-abdominal bleeding and has similar sensitivity in the pregnant and nonpregnant individuals (40). The finding of free fluid in blunt trauma in pregnancy indicates a higher intra-abdominal injury rate, noting that free fluid is not necessarily a normal or physiologic finding of pregnancy (41). At one institution, FAST was additionally used as a screen for pregnancy where 18 of 144 (11%) of female patients were newly diagnosed with pregnancy prior to a pregnancy test (42). With diagnosis of pregnancy, FAST contributed to a significant decrease in fetal radiation exposure when compared to other trauma patients diagnosed with pregnancy by serum human chorionic gonadotropin (HCG) screening (42). However, FAST and US are of limited value in the diagnosis of placental abruption after trauma and may provide false-negative results in up to 50% to 58% of cases. The vascular nature of the placenta may have the same echogenicity as blood, so identification of retroplacental bleeding is not always possible (43,44).

Graded compression ultrasonography (GCUS) is still the initial test of choice in the assessment of appendicitis during pregnancy, despite a low sensitivity for diagnosis of 20% to 36% (45). Imaging is approximated on the self-reported area of maximal pain as McBurney’s point changes based on the size of the uterus (46) with diagnostic criteria of a dilated (≥7 mm), fluid-filled, noncompressible, blind-ending tubular structure (45). MRI is the second preferred modality for evaluating appendicitis in pregnancy with sensitivity of 96.8%, specificity of 99.2, accuracy of 99%, PPV of 92.4%, NPV of 99.7% (47). CT scan is reserved for those patients for which a rapid and accurate diagnosis is required, to prevent the potential dangerous sequelae of appendix rupture.

Imaging of the biliary tract is similar to that of the nonpregnant patient. Acute cholecystitis detection using US with findings of cholelithiasis, gallbladder wall thickening, pericholecystic fluid, and Murphy’s sign confers a 94% PPV compared to 88% when gallstones are present in isolation (45). Magnetic resonance cholangiopancreatogram (MRCP) is the appropriate second-line agent to evaluate for biliary disease approaching 98% sensitivity and 94% specificity for biliary tract disorders. Endoscopic retrograde cholangiopancreatography (ERCP) typically is utilized only if therapeutic intervention is expected or necessary, as it does expose the patient to ionizing radiation and is associated with several potential complications (45).

Magnetic Resonance Imaging

MRI has become a useful tool to identify the source abdominal pain in clinically stable pregnant patients. It is considered a safe modality in all trimesters of pregnancy, but due to thermal increases of imaging tissue during the MRI, there is a theoretical fetal teratogenic risk during the first trimester (37). Additionally, paramagnetic contrast agents such as gadolinium can cross through the placenta and enter the fetal circulation, and have proven higher rates of spontaneous abortion, skeletal abnormalities, and visceral abnormalities in animals when given as a dose two to seven times the normal dose. There have not been any reports of human teratogenicity. This agent should be used in pregnancy only if it provides substantial benefit over potential risk (38,48). Given the theoretical fetal risks, it is recommended to consent for this procedure (48). A clinician should use MRI with the knowledge that it is time consuming and challenging to evaluate an unstable patient while undergoing the examination and is reserved for clinically stable patients (38). MRI has been a useful imaging technique for appendicitis, inflammatory bowel disease, pancreatitis, intussusception, hydronephrosis and pyelonephritis, fibroids (and fibroid degeneration), adnexal masses (49), and placental abnormalities (accreta, perceta, increta) (49). MRI studies confirm that the appendix and cecum are superiorly displaced as pregnancy advances (46) and more reliably identifies the appendix than does US, with a sensitivity approaching 100% (49–51).

Computed Tomography

CT may be considered for evaluation of the abdomen if other studies are equivocal or unavailable, for blunt trauma, or as a triaging tool to prevent delays in treatment. The radiation dose can be reduced to limit excessive ionizing radiation exposure to the fetus, and as the doses are cumulative, it is suggested to avoid repeated studies if clinically appropriate (45,52,53).

Angiography

Ionizing radiation with fluoroscopy presents at about 100 mGy/min (24) and should be used with caution in pregnancy, particularly in the use of evaluating and treating pelvic bleeding. Abdominal shielding and limiting fluoroscopy time should be considered when performing this procedure. It is currently not recommended to use embolization techniques directly to the pregnant uterus (6). Alternatives to treat pelvic bleeding include laparotomy and preperitoneal packing with possible external fixation of the pelvis (54).

Trauma

Trauma complicates 1 in 12 pregnancies and is the leading cause of nonobstetric death under 40 years of age, accounting for 46% of maternal deaths in the United States. The mean age for trauma is 24 years old with a mean gestation of 25.9 wGA and is caused by motor vehicle accidents (55%), falls (23%), assaults (22%), and burns (1%) (6,55). Sequelae can lead to significant maternal morbidity with higher incidence of spontaneous abortion, preterm premature ROM, preterm birth, uterine rupture, cesarean delivery, placental abruption, and stillbirth. Approximately 5% to 24% of patients admitted for trauma will deliver during the same admission, suggesting that these patients should be transported to a center that provides trauma, obstetric, and neonatal service lines (5,6,56). Identified risk factors for traumatic accidents include younger women (<25 years old), African Americans, Hispanics, underinsured (5), use of illicit drugs or alcohol, history of domestic violence, and noncompliance to seatbelt use (6) (Table 80.3).

TABLE 80.3 Trauma Team Personnel for the Pregnant Individual

The immediate goal for a pregnant trauma patient is to stabilize the mother first, as fetal outcomes are dependent on early and aggressive maternal resuscitation (56). The primary survey includes the evaluation and prompt treatment of the maternal airway, ensuring adequate ventilation and oxygenation, and effective circulatory volume. In the event of cardiac arrest, prompt initiation of advanced cardiac life support (ACLS) should be performed with slight alterations described below. It is important to note that the maternal physiologic manifestation of increased plasma volume and red blood cell mass will allow more blood loss prior to changes in the maternal vital signs, but fetal perfusion may be impaired. Uterine compression of the vena cava can reduce blood return to, and preload of, the heart. Therefore, in gestations beyond 20 wGA the uterus needs to be displaced upward and leftward by either a 15- to 30-degree left lateral tilt or manual displacement upon its recognition. Spinal precautions and C-spine mobilization should be maintained through the uterine displacement process if indicated. An assessment of disability and exposure of the patient for a full primary survey is paramount prior to approaching the fetal status, which is typically performed in the secondary survey (except for in instances of obvious uterine hemorrhage, then prompt measures to correct the circulatory volume and address the bleeding is in the primary survey) (57).

The secondary survey (Table 80.4) immediately follows the primary survey, the initial resuscitation, and initial adjuncts to care such as cardiac monitoring, blood pressure monitoring, pelvic binding or shock trousers, and pulse oximetry. During the secondary survey, pregnancy should be assessed by history, physical examination, HCG (urine or blood) in women of childbearing age, and possibly by the FAST. The entire trauma team should be made aware of pregnancy status, have placement of intravenous access above the diaphragm as pelvic compression may limit resuscitative medications and fluids to the circulatory volume. All indicated traumatic bedside procedures can be performed as indicated with consideration to alter technique (57). A diagnostic peritoneal lavage can be preferably performed above the umbilicus and fundus in a pregnancy beyond 20 wGA to avoid uterine instrumentation, usually performed after gastric decompression. Additionally, chest tubes should be placed one to two rib spaces above its normal placement of above the fifth rib, to prevent abdominal entry (56). A limited obstetric US should be performed by an experienced provider to determine fetal number, viability, size and gestational age, position, and evaluation of placenta for abruption and uterus for rupture. Continuous fetal monitoring should ensue if the gestation is beyond 20 wGA by means of a fetal cardiotocometry (heart rate monitor and monitor for contractions). An assessment of labor and ROM should be performed by history, physical examination, sterile speculum examination, cervical examination, and other adjunctive tests as indicated. Consultants may include an obstetrician, anesthesiologist, neonatologist, and/or pediatrician (57).

TABLE 80.4 Trauma’s Secondary Assessment in the Pregnant Woman

Treatment of the pregnant trauma patient should be virtually identical to a non-pregnant patient with several specific alterations. Usage of all diagnostic modalities, including CT scan should be performed if indicated. Placing abdominal shielding and attenuating the dose of radiation may help reduce unnecessary radiation exposure to the fetus if feasible to achieve the appropriate image. CT of the head and neck involves very low fetal exposure and should be performed as per routine hospital protocols (58). If avoidance of ionizing radiation (CT and radiography) is plausible, then alternative methods to diagnosis should be employed. In addition to the aforementioned consultants, a pharmacist should review medications prescribed to prevent unnecessary administration to the fetus. However, there are very few medications that need to be withheld for treatment of the pregnant woman. In case of the need for an emergent delivery for fetal or maternal indications, the medical center should ensure that clinicians have easy and prompt access to a neonatal warmer and resuscitation kit, cesarean section surgical kit, and fetal monitoring system. These items should be with the patient at all times (intensive care unit, operating room, imaging suite, etc.).

The obstetrician as a consultant should remark on the following:

1. If the patient is Rh negative, a Kleihauer–Betke (KB) test and 300 μg of Rh-D immunoglobin (Rh-D Ig) should be administered within 72 hours of the trauma. An additional dose of Rh-D Ig 300 μg should be given to all Rh-women for every additional 30 mL of fetal blood found on KB testing, to prevent isoimmunization of the mother that can have deleterious effects on a subsequent pregnancy (12).
   
2. If the patient is between 24 and 34 wGA and a preterm birth is anticipated in the next 7 days, consideration for administration of antenatal corticosteroids and tocolysis may be indicated.
   
3. There should be comments on fetal status, indicated length of monitoring, appropriate positioning to monitor of the fetus and patient, and determination for further fetal evaluation with ultrasound.
   
4. Depending on the maternal and fetal conditions, the consultant should comment on timing and recommended route of delivery, patient disposition, and outpatient follow-up.
   
5. The consultant should obtain records or directly obtain routine prenatal labs, cultures, and diagnostics, as well as group B streptococcal screening and treatment if indicated. Of note, routine KB tests have been widely adopted in the trauma assessment; however, it has a poor predictive value of fetal distress or death, preterm birth, placental abruption, and typically does not alter management (12,56). Its utility has remained in aiding the calculated amount of Rh-D Ig to administer.

Duration of fetal monitoring recommendations after minor and major trauma is still controversial, and there is a lack of level I evidence for management guidelines. However, the EAST Practice Management in 2010 developed several level II and III guidelines to guide the clinician for appropriate duration of monitoring: “All women >20 week gestation who suffer trauma should have cardiotocographic monitoring for a minimum of 6 hours. Monitoring should be continued (for 24–48 hours) and further evaluation should be carried out if uterine contractions (>1 contraction per 10 minutes), a nonreassuring fetal heart rate pattern, vaginal bleeding, significant uterine tenderness or irritability, serious maternal injury (Injury Severity Score [ISS] >9, ejection from motor vehicle, motorcycle or pedestrian accident), or ROM is present” (59).

The rationale for extended fetal monitoring in the above criteria is that screening modalities such as history, physical examination, and obstetrical ultrasound are poor predictors for placental abruption, preterm labor, and fetal death. In a retrospective study, there was a higher rate of placental abruption for patients in motor vehicle accident ejections, maternal tachycardia above 110 beats/min, ISS over 9, or fetal bradycardia or tachycardia, suggesting a minimum of 24 hours of monitoring in this cohort of patients (43). Older studies have noted that placental abruption did not occur in trauma patients with less than one contraction every 10 minutes when monitored for a 4-hour period (12,44,60). Many hospitals follow the guideline for a minimum of 4 to 6 hours of cardiotocographic monitoring for patients who do not meet the above criteria for extended monitoring.

Five percent to 24% of pregnant patients admitted for trauma deliver during that hospitalization and usually within 24 hours of the trauma. This is likely a result of placental abruption causing uteroplacental insufficiency and fetal distress, activating the labor process (6). In studies that include route of delivery after trauma, about 75% of all deliveries are performed by cesarean section (5,6). The route of delivery is decided by routine obstetric guidelines in addition to the following conditions. Pelvic fracture is not an absolute contraindication to vaginal delivery, even in highly displaced pelvic fractures or hardware placement. However, large dislocating or unstable fractures may prohibit an attempt at vaginal delivery, and may require a cesarean delivery (12,61). Delivery induction is recommended for patients suffering burns over 40% of the body because of the high fetal mortality rate, aggressive fluid resuscitation, high need for ventilatory support, and high suspicion for thrombosis and/or sepsis (62,63). In burns, an early delivery may improve maternal condition and prevent fetal death (Fig. 80.1).

Fortunately, severe trauma requiring admission to the ICU is infrequent (3 in 1,000 pregnancies). It is estimated that 1,300 to 3,900 fetuses are lost due to maternal trauma each year. Mild maternal injuries carry a 1% to 5% fetal loss rate, whereas life-threatening trauma is associated with loss rates up to 40% to 50%. Because mild trauma is more prevalent, most fetal loss is due to minor maternal injury (12). Pregnant patients with pelvic or acetabular fractures are associated higher maternal and fetal death rates, 9% and 35%, respectively (64). The high fetal mortality rate is likely due to concentration of force enough to break the maternal pelvis, which is likely to also impact the fetus directly. As such, in penetrating abdominal injuries at the level of the uterus has a higher fetal mortality rate, but actually has a reduced maternal mortality rate, presumably as the uterus shields other vital maternal organs (7,65). Population-based data indicate that motor vehicle crashes account for 82% of fetal deaths after trauma, with an overall rate of 3.7 per 100,000 live births. The highest rate of fetal death due to trauma is seen in patients between 15 and 19 years of age (11,66).

Acute Abdomen

Acute abdominal pain in the pregnant female is a very common complaint. Although most times it can be attributed to labor, round ligament pain, constipation, urinary tract infection, or gastrointestinal reflux, it is important to obtain an appropriate history and physical examination to screen for life-threatening disease. The diagnosis can be difficult as some complaints may start with vague symptomatology, compounded with the hesitancy of a clinician to perform invasive or radiologic procedures due to fear of fetal safety. The most common diagnosis yielded from “abdominal pain” nearing a term gestation is labor that typically presents with regular and increasing frequency of abdominal cramping, pelvic pressure, bloody or fluid vaginal discharge. Although it not characteristic to have rebound abdominal tenderness in labor, syndromes such as chorioamnionitis and placental abruption may cause exquisite fundal tenderness, further disguising an underlying surgical disease. Another confounding factor is that both term and preterm labor can be precipitated from these acute abdominal processes, necessitating the clinician to recognize an abdominal illness in addition to labor (67). In a recent patient survey and chart review, the highest nonobstetric complaints lead to diagnoses of biliary ascariasis (28%), peptic ulcer disease (24%), lower urinary tract infection (10%), acute pyelonephritis (6%), acute gastroenteritis (6%), acute cholecystitis (6%), acute appendicitis (6%), renal colic (4%), choledocolithiasis (3%), acute pancreatitis (2%), ovarian solid mass (2%), torsed ovarian mass (2%), and renal calculus (1%) (68). This section will focus on surgical diseases of the abdomen in pregnancy, which is estimated to occur in about 1 per 635 pregnancies (67).

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