UPDATE ON OBSTETRICS
New guidance on timing of elective delivery, screening for thrombophilias, and use of magnesium sulfate for fetal neuroprotection
IN THIS ARTICLE
When a thrombophilia is detected in these settings, the practitioner faces a dilemma—namely, what to do when the mother is otherwise healthy and asymptomatic. All too often the finding of a thrombophilia leads to the initiation of some anticoagulation regimen, ranging from low-dose aspirin all the way to therapeutic anticoagulation with heparin.
Over the past year, several studies and expert opinions have been published that recast the role of thrombophilia screening in obstetric practice.
Writing for the Maternal-Fetal Medicine Units (MFMU) Network, Silver and colleagues concluded that the prothrombin (PT) gene mutation G20210A was not associated with pregnancy loss, preeclampsia, fetal growth restriction, or placental abruption in a low-risk, prospective cohort.
Said and coworkers reached a similar conclusion. In a blinded, prospective cohort study, they screened for the following mutations in 2,034 healthy nulliparous women before 22 weeks’ gestation:
- factor V Leiden mutation
- PT gene G20210A mutation
- methylenetetrahydrofolate reductase enzyme (MTHFR) C677T
- MTHFR A1298C
- thrombomodulin polymorphism.
The majority of asymptomatic women who carried an inherited thrombophilia polymorphism had a successful pregnancy outcome. In fact, homozygosity of the MTHFR A1298C mutation was found to be protective.
Population-based screening for thrombophilias is not recommended. In fact, some authors have advised against screening for thrombophilias even in the setting of a thrombotic event, suggesting it has limited utility.3
The main reason to screen for a thrombophilia at this time is to explore idiopathic thrombosis or a strong family history of the same. There is no need to screen for thrombophilias when the patient has a history of pregnancy loss, placental abruption, preeclampsia, and fetal growth restriction.
If you give magnesium sulfate for fetal neuroprotection, adhere to a protocol
ACOG Committee Opinion No. 455: Magnesium sulfate before anticipated preterm birth for neuroprotection. Obstet Gynecol. 2010;115(3):669–671.
Magnesium sulfate has a long and glorious history in obstetrics, having been used to prevent eclampsia, to treat preterm uterine contractions, and now, potentially, to reduce the incidence of central nervous system damage among prematurely delivered infants.
Cerebral palsy (CP) is most commonly associated with prematurity and intrauterine fetal infection. Only in the past two decades has there been a shift away from assigning the cause of most cases of CP to intrapartum events. Nevertheless, CP remains an important concern among patients and providers, and research continues to find ways to prevent CP or minimize its effects.
Numerous large trials have explored the use of magnesium sulfate to prevent CP in preterm infants. Although their findings have not been as definitive as researchers had hoped, some data do suggest that magnesium sulfate has a protective effect.
The American Congress of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) urge caution in regard to the use of magnesium sulfate for fetal neuroprotection. The SMFM points out that the reported benefits of magnesium sulfate in this setting have been derived largely from secondary analyses. The SMFM recommends that, if magnesium is used at all, it should be administered according to one of the published protocols (three are cited in the ACOG opinion).
The SMFM goes on to warn against choosing magnesium sulfate as a tocolytic solely because of its possible neuroprotective effects.
In a Committee Opinion published last year, ACOG was a bit more definite. “The Committee on Obstetric Practice and the Society for Maternal-Fetal Medicine recognize that none of the individual studies found a benefit with regard to their primary outcome,” the opinion states. “However, the available evidence suggests that magnesium sulfate given before anticipated early preterm birth reduces the risk of cerebral palsy in surviving infants. Physicians electing to use magnesium sulfate for fetal neuroprotection should develop specific guidelines regarding inclusion criteria, treatment regimens, concurrent tocolysis, and monitoring in concordance with one of the larger trials.”
Recent editorials have cautioned against using magnesium sulfate for fetal neuroprotection until more data become available,4 or have left it up to the individual practitioners (or institution) to decide whether it is advisable.5
The use of magnesium sulfate for fetal neuroprotection when preterm delivery seems likely requires additional research. For now, this practice should be governed strictly by protocol. And it should not be viewed as “standard of care” by our legal colleagues.
When administering magnesium sulfate, avoid giving a cumulative total in excess of 50 g, as this amount may increase the risk of pediatric death.6
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