Ucyigit A, Fuller JL, Poon LC, et al. - Researchers conducted a non-interventional retrospective cohort study of 1,056 patients spanning a 14-year period with the aim to determine if an association exists between low initial serum progesterone, sonographic parameters and clinical outcomes in women presenting with pregnancies of unknown location (PUL), which are identified to be ongoing at their follow up scans in the first trimester. Per findings, a tendency towards smaller gestational sacs (GS) was identified in pregnancies with low progesterone compared with those with a higher progesterone, and the GSs are smaller than expected for a given crown-rump length (CRL). The risk of miscarriage was noted to be higher for women with low progesterone at the start of pregnancy, even when the pregnancy is initially identified as viable in the first trimester. In addition, these pregnancies tend to be linked with the sonographic finding of a smaller GS than expected for a given gestational age; this is noted irrespective of eventual outcome.