Chemical pregnancies: immunologic and ultrasonographic studies

Implantation of the embryo determines successful from unsuccessful cycles after in vitro fertilization (IVF) and embryo transfer (ET). The purpose of this study was to compare immunologic risk factors among women experiencing implanation failure characterized by a negative pregnancy test after IVF/ET and those experiencing chemical pregnancies. In addition ultrasonographic measurement of gestational sac size from 24 to 35 days from last menstrual period (LMP) were compared between chemical pregnancies and other pregnancy outcomes.

Blood samples from 122 women experiencing IVF implantation failure with a negative pregnancy test after ET and 20 women with chemical pregnancies were evaluated for the presence of antiphospholipid antibodies (APA), antinuclear antibodies (ANA), circulating embryotoxins (ETA) and elevated levels of natural killer (NK) cells. Gestational sac size measured from 24 to 35 days form LMP were compared according to pregnancy outcome: term birth (n = 46), ectopic pregnancy (n = 49), spontaneous abortion (n = 56) and chemical pregnancy (n = 20).

Women experiencing chemical pregnancies had a higher frequency of APA than women with implantation failure associated with a negative pregnancy test (80% versus 28%, P < 0.0001). The prevalence of ANA, elevated NK cells and ETA was not different between the two groups. The mean gestational sac size from 24 to 35 days from LMP did not differ when chemical pregnancies were compared with pregnancies progressing longer than 35 days. The maximal gestational sac diameter among chemical pregnancies was 3.8 mm.

Mechanisms involved in implantation failure associated with a negative pregnancy test may be different from those involved in chemical pregnancies. Chemical pregnancies may be the result of defective angiogenesis.