Fetal cardiac development and hemodynamics in the first trimester

Objective To describe fetal cardiac and hemodynamic development in the firs t trimester of pregnancy. Subjects and methods Forty-eight pregnancies were prospectively studied wit h transvaginal ultrasound and color Doppler. Fetal heart rate and size tr,e re documented together with the presence of inflow and outflow waveforms an d valve signals. Results Heart rate and size showed a positive correlation with gestational age. At 6 weeks of gestation, 20% of the cardiac cycle was occupied by the isovolumic contraction time (ICT); the isovolumic relaxation time (IRT) occ upied 16% and remained unchanged, while the ICT progressively shortened and was not measurable after 12 weeks. The peak inflow velocities had changed from monophasic to biphasic by 10 weeks of gestation. At 7 weeks of gestati on, semilunar valves were detected in 10% of examinations and the atriovent ricular valves in 3%. The detection rate for both valves at 12 weeks was gr eater than or equal to 90%. In pregnancies that miscarried, the detection r ate for both was <25%. Conclusions The Doppler signals that characterize the heart during the firs t trimester suggest effective heart compliance by 12 weeks. Normal valve de velopment can be inferred from non-invasive Doppler recordings.