Etiology and evaluation of stillbirth in patients with obesity

Abstract

Objective Maternal obesity is a risk factor for stillbirth, but whether or not the etiology of stillbirth differs in gravidas with and without obesity is unknown. We categorized stillbirths in a contemporary cohort to test the hypothesis that the etiology of stillbirth is different in gravidas with and without obesity. Methods This retrospective cohort study included all gravidas with a stillbirth ≥20 weeks’ gestation between 2010 and 2017 and a normal mid-trimester anatomic survey by ultrasound assessment at a large academic institution. Pregnancies were excluded if delivery data were unavailable, a multifetal gestation was present, or there was an antenatally diagnosed fetal structural or genetic anomaly. Our primary exposure was maternal obesity, defined as a body mass index (BMI) ≥ 30 kg/m2 at the time of anatomic survey. Our primary outcome was stillbirth etiology, as classified by the initial causes of fetal death tool from the Stillbirth Collaborative Research Network and includes maternal, obstetric, hematologic, fetal, infectious, placental, other, or unexplained categories. Our secondary outcomes included the evaluation performed on each stillbirth, compliance with the recommended stillbirth evaluation by the American College of Obstetricians and Gynecologists (ACOG), and the percentage of abnormal results for each of the tests ordered for stillbirth evaluation. Results Of 118 stillbirths meeting the inclusion criteria, 44 (37.3%) occurred in gravidas with obesity and 74 (62.7%) were in patients without obesity. An obstetric complication was the most commonly identified etiology for stillbirth, found in 40.9% of cases with obesity versus in 29.7% of cases without obesity (aOR 1.09, 95% CI 0.47–2.66). The likelihood of any specific etiology of stillbirth was not significantly different in gravidas of the two weight groups, after controlling for confounders. However, assignment to the unexplained stillbirth category was significantly less common in women with obesity, compared to those without obesity (aOR 0.18, 95% CI 0.05–0.67). There was no difference in testing performed on each stillbirth between the groups. Compliance with the ACOG-recommended diagnostic evaluation for stillbirth was similar in the two groups but was only performed in 10.2% of all cases of stillbirth. Placental pathology was the test most likely to yield an abnormal result in both groups, but the percentage of abnormal results for this and all other tests was the same in the presence and absence of obesity. Conclusion There is no specific etiology of stillbirth seen in gravidas with obesity, compared to those without obesity, after controlling for maternal confounders. We surmise that the evaluation recommended for stillbirth assessment in the general population is appropriate for stillbirth evaluation in gravidas with obesity. Testing pursued was similar between groups, but compliance with ACOG recommendations for testing after stillbirth was deficient in the cohort. Future work should aim to identify and address barriers to completing the recommended stillbirth evaluation.