To study the association between initial fetal crown-rump length and subsequent abortion in a viable first trimester pregnancy

Abstract

Background: Ultrasonography is one of the most important and useful diagnostic tool in the field of modern medicine. In the 1st trimester fetal crown rump length correlates closely with gestational age and is often used as the gold standard for dates. It provides the most accurate estimate of gestational age and crown rump length at 6-10 weeks predicts the due date with an accuracy of ±3 days. The objective of the study is to study the association between initial fetal crown-rump length (CRL) and subsequent abortion in a viable first trimester pregnancy.Methods: Hospital based analytic type of observational study was conducted in a tertiary care maternity hospital. The recruited participants were young pregnant women at 6-10 weeks of viable gestation. Transvaginal ultrasonography was performed to determine pregnancy viability and measure the embryonic CRL.75 first trimester pregnancy cases with normal initial crown-rump-length and 75 first trimester pregnancy cases with deficit initial crown-rump-length were taken. The deviation of observed and expected CRL was calculated and expressed in standard deviations (SD) as Z- score. The primary outcome measure was the percentage of pregnancies with antecedent growth delay that aborted by the end of the first trimester.Results: In 150 women who met with the inclusion criteria, the pregnancy remained viable in 97 (64.66%) and 53 (35.34%) suffered abortion. At the first transvaginal ultrasound, the mean Z- score for CRL was significantly lower in pregnancies that subsequently aborted compared to pregnancies that remained viable (-0.613 vs 0.335 , respectively, P <0.001). Among 75 cases of normal CRL 65 (86.67%) remained viable and 10 (13.33%) aborted and in deficit CRL 32 (42.67%) cases remained viable and 43 (57.33%) aborted. Out of 53 pregnancies which aborted 43 (81.13%) had deficit CRL. Significant difference was present (P <0.001, significant).Conclusions: We infer that a deficit in initial fetal CRL in a viable first trimester pregnancy has a significant positive association with subsequent abortion. With increasing deviation of observed CRL from the expected CRL the risk of subsequent abortion increases.