Progesterone is a hormone critical to the maintenance of early pregnancy, yet there is a lack of an established distribution of progesterone levels in early pregnancy. This study aims to establish the distribution of maternal serum progesterone in normal pregnancies and pregnancies complicated by threatened miscarriage. We hypothesize that progesterone deficiency is associated with threatened miscarriage.
This is a single center, prospective cohort study of 718 women. Women from the normal pregnancy group were recruited from routine antenatal clinics and those in the threatened miscarriage group were recruited from emergency walk-in clinics.
Quantile regression was used to characterize serum progesterone levels in these two groups by estimating the 10th, 50th and 90th percentiles from 5 to 13 weeks gestation. Pregnancy outcome was determined at 16 weeks. Subgroup analysis within the threatened miscarriage group, to compare progesterone levels of women who miscarried with those with viable pregnancies was performed.
Serum progesterone demonstrated an increasing linear trend in the normal pregnancy group, with trend gradient of bN = 4.62 (P < .0001). In the threatened miscarriage group, a linearly increasing trend with reduced gradient of bT= 4.55 (P< .0001) was observed. Median progesterone levels were consistently lower in this group by 10 nmol/L.
Maternal serum progesterone concentration increased linearly with gestational age from 5 to 13 weeks in normal pregnancies. In women with threatened miscarriage, a downward displacement of this linear association was observed. This highlights the association between progesterone deficiency and threatened miscarriage.