Differentiation of genetic abnormalities in early pregnancy loss.

OBJECTIVE: To characterize the types of genetic abnormalities and their prevalence in early pregnancy loss at different developmental stages. We hypothesized that the prevalence of genetic abnormalities in pregnancy loss would differ across developmental stages.

METHODS: Women with a pregnancy loss at < 20 weeks' gestation (n = 86) were enrolled at the time of diagnosis. Maternal tissue without a fetal component was found in 13 samples. Chromosomal microarray analysis (CMA) was performed on 74 samples (including two samples from a twin pregnancy); 15 were pre-embryonic (no visible embryo on ultrasound examination), 31 were embryonic (embryo; 6 + 0 to 9 + 6 weeks' gestation) and 28 were fetal (fetus; 10 + 0 to 19 + 6 weeks' gestation) losses. The twin pregnancy was found to be monochorionic diamniotic and was subsequently treated as a single sample in our analysis. Nine samples that underwent CMA were excluded from analysis because of 100% maternal-cell contamination.

RESULTS: The overall prevalence of genetic abnormalities differed across developmental stages (9.1% pre-embryonic, 69.2% embryonic and 33.3% fetal; P < 0.01). This difference persisted when comparing pre-embryonic with embryonic samples (P < 0.01) and embryonic with fetal samples (P = 0.02) but not pre-embryonic with fetal samples (P = 0.12). Additionally, the prevalence of aneuploidy differed significantly across developmental stages (0.0% in pre-embryonic samples vs 65.4% in embryonic samples vs 25.9% in fetal samples, P < 0.001). Abnormalities were most common in embryonic cases, followed by fetal and then pre-embryonic. Maternal cell contamination (MCC) was noted in 47.4% of 46,XX cases assessed.

CONCLUSIONS: Genetic abnormalities detected by CMA are more likely to occur in the embryonic period than in pre-embryonic or fetal stages. MCC is common in early pregnancy loss and should be excluded when results demonstrate a 46,XX karyotype.