First and second trimester maternal serum markers in pregnancies with a vanishing twin.

Objective: The aim of this study was to assess the concentration of the first and second trimester maternal serum markers in pregnancies with a vanishing twin.

Methods: This is a retrospective case-control study of pregnancies screened for Down syndrome in one Ontario center. Singleton pregnancies with ultrasound evidence of a vanishing twin were identified, and each was matched with five normal singleton controls for ethnicity, maternal age, gestational age, and blood sampling date.

Second trimester prenatal screening for Down syndrome: the associations between the levels of serum markers in successive pregnancies.

Objective: To investigate the association of Down syndrome screening results in successive pregnancies, and assess the impacts of including previous screening results in the current risk estimation on screening performance.

Methods: The study was based on 56,951 women who had triple marker screening in two or more singleton pregnancies in the Ontario Maternal Serum Screening (MSS) program between October 1993 and September 2000. The problem of recurrent false positive results was examined by comparing screening results from different pregnancies in the same individuals.