Clinical Review

UPDATE ON OBSTETRICS

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New guidance on timing of elective delivery, screening for thrombophilias, and use of magnesium sulfate for fetal neuroprotection


 

References

DID YOU SEE THESE BEST-READ OB ARTICLES?

From an evolutionary standpoint, not much has changed in pregnancy and childbirth. From a clinical perspective, however, flux is a constant. Three issues, in particular, have seen notable development over the past year:

  • optimal timing of elective delivery
  • screening for thrombophilias in women who experience recurrent pregnancy loss, fetal growth restriction, preeclampsia, or placental abruption
  • use of magnesium sulfate for fetal neuroprotection.

Of course, in the specialties of obstetrics and perinatal medicine, research continues in a variety of other subject areas, as well. Simulation training, diagnosis and management of gestational diabetes, and rescue steroid treatment are three examples. Other issues being explored include the use of progesterone to prevent prematurity, the use of ultrasonography to measure cervical length, and the safety of vaginal birth after cesarean delivery. The three areas highlighted here are not the only ones “ready for prime time,” but they are areas of considerable interest and debate.

We have a tradition in obstetrics of not embracing change too quickly. We learned this lesson through our experience with diethylstilbestrol (DES) and thalidomide, and we must continue to use caution whenever new technologies or management approaches are proposed.

30 weeks is the rule, provided delivery is truly elective

Tita ATN, Landon MB, Spong CY, et al. Timing of elective cesarean delivery at term and neonatal outcomes. N Engl J Med. 2009;360(2):111–120.

When it comes to elective delivery, no one would argue against the wisdom of continuing pregnancy until at least 39 weeks’ gestation in the absence of complications. But what data form the basis of this wisdom, and when might it be prudent to consider earlier delivery?

In a widely publicized study, Tita and colleagues concluded that elective repeat cesarean delivery before 39 weeks of gestation (i.e., 37 through 38-6/7 weeks) is associated with a higher rate of neonatal respiratory distress and other adverse neonatal outcomes than is delivery at 39 to 40 weeks. Note, however, that the primary outcome of this study was a composite. Therefore, the findings should be interpreted with some caution.

In their report, Tita and coworkers acknowledged that the transient and predominantly minor complications associated with delivery before 39 weeks must be weighed against the risk of fetal death inherent in delaying delivery through 38 full weeks—and an accompanying editorial made the same point.1 Stillbirth occurs at a rate of 1 case for every 1,000 births in the 37- to 39-week gestational age range—a rate that may be higher than the risks associated with delivery. Even so, the risk of stillbirth at 37 to 39 weeks is very small, and that risk is unlikely to be lowered through routine antenatal fetal testing. We should also remember that the risks of neonatal respiratory distress, transient tachypnea, admission to the neonatal intensive care unit (NICU), and even cerebral palsy2 may be increased with delivery at 37 to 38 weeks, or at 42 weeks or later, compared with delivery at 40 weeks.

WHAT THIS EVIDENCE MEANS FOR PRACTICE

All truly elective deliveries should occur at or after 39 weeks of gestation. However, when indicated, earlier delivery is acceptable—even essential—if we are to minimize maternal and neonatal morbidity and mortality in high-risk circumstances, such as hypertensive disorders of pregnancy, placenta previa, fetal growth restriction, and other conditions.

Investigations are under way to determine whether there is a role for routine betamethasone administration (regardless of indication or gestational age) in the absence of labor before 39 weeks. Until those data come in, we should continue to follow current practice guidelines for antenatal maternal administration of betamethasone—namely, a single course given between 24 and 34 weeks in women who have an elevated risk of preterm delivery.


Population-based screening for thrombophilias is not recommended

Silver RM, Zhao Y, Spong CY, et al, for the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units (NICHD MFMU) Network. Prothrombin gene G20210A mutation and obstetric complications. Obstet Gynecol. 2010;115(1):14–20.

Said JM, Higgins JR, Moses EK, et al. Inherited thrombophilia polymorphisms and pregnancy outcomes in nulliparous women. Obstet Gynecol. 2010;115(1):5–13.

Since the mid-1990s, screening for thrombophilias has been recommended in the evaluation of a variety of adverse reproductive outcomes, including, but not limited to:

  • recurrent pregnancy loss
  • unexplained stillbirth
  • placental abruption
  • preeclampsia
  • fetal growth restriction.

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