940 Frequency of and indications for preterm birth in pregnancies with non-immune hydrops fetalis spectrum disorder

Abstract

Non-immune hydrops fetalis (NIHF) is associated with poor perinatal outcomes, including preterm birth (PTB). However, the frequency and causes of PTB are not well understood. We hypothesize that PTB is common and frequently iatrogenic in pregnancies complicated by NIHF spectrum. Secondary analysis of a prospective cohort of singleton pregnancies with NIHF spectrum. NIHF spectrum was defined as: isolated nuchal translucency (NT) ≥3.5mm, or 1 or ≥2 effusions (pleural effusion, pericardial effusion, ascites, and/or skin edema). The primary outcome was frequency of PTB (<37 weeks). Secondary outcomes were reasons for PTB (spontaneous, iatrogenic for maternal or fetal indication), PTB by type of effusion(s) and presence of genetic diagnosis. Multivariable logistic regression generated adjusted odds ratios (aOR). Among 152 cases of NIHF spectrum enrolled between 10/2018 and 7/2020, 68 did not result in termination, early spontaneous loss, or stillbirth. Of these, 76% (52/68) delivered preterm at a median gestational age of 33.4 weeks (IQR 30.9-36.5). Among the 52 PTBs, 19 (36.5%) were spontaneous, 9 (17.3%) were iatrogenic due to maternal indications (primarily pre-eclampsia), and 24 (46.2%) were iatrogenic due to fetal indications (primarily non-reassuring antenatal testing or worsening NIHF). PTB occurred in 9.1% (1/11), 77.8% (7/9), and 91.7% (44/48) of isolated enlarged NT, 1 effusion, and ≥2 effusions, respectively (figure). A genetic diagnosis was present in 36.5% of cases with PTB, compared to 18.8% who delivered at term (aOR 2.8, 95% CI 0.4-21.1). Polyhydramnios complicated 50.0% of all PTBs versus only 6.3% of term births (aOR 15.8, 95% CI 1.1-229.8). Pregnancies with 1 or ≥2 effusions frequently result in PTB, most often iatrogenic due to non-reassuring fetal status. Additionally, PTB was observed more frequently in cases with a genetic diagnosis and with polyhydramnios. These data are informative for counseling patients as well as for developing strategies to reduce PTB in this population.