Ovarian cysts

The widespread use of ultrasound in the first trimester for dating and for viability and nuchal fold assessment has increased the detection of ovarian masses. Before the advent of such intensive imaging, clinicians would only become aware of ovarian cysts in pregnancy when they became symptomatic or clinically palpable.

Small ovarian cysts are common in the first trimester of pregnancy, the majority of which arise from a functional corpus luteum or a redundant follicle. These physiological cysts are typically asymptomatic and impalpable, and are often incidental findings at routine first-trimester ultrasound.

In a prospective observational study of 6600 pregnancies in a single institution in Italy, the frequency of ovarian cysts larger than 3 cm was 1.2%, with 51% of these cysts resolving during pregnancy. In a similar UK series, 3000 consecutive 14 week scans demonstrated the presence of ovarian cysts in 5.3% of pregnancies, and 71% resolved spontaneously. There are variations between the studies in the diagnostic criteria for ovarian cysts but nevertheless these data demonstrate how common they are in the first trimester. As might be expected, the discovery of simple cysts declines as the corpus luteum loses its function.

The natural history of such cysts is to gradually resolve over the course of the pregnancy, with most doing so by 16 weeks of gestation.