Data and sample collection

EFPTS has several unique features: it is population-based and prospective, with the possibility of long-term follow-up.

The twins (and higher-order multiple births) are recruited at birth; basic perinatal data recorded; chorion type and zygosity established; and since 1969 placental biopsies have been taken and frozen at −80 ◦C for later determination of genetic markers.

East-Flanders Prospective Twin Survey (EFTPS)

The EFPTS is the only large register that includes placental data and allows differentiation of three subtypes of monozygotic (MZ) twins based on the time of the initial zygotic division: the dichorionic–diamniotic pairs (early, with splitting before the fourth day after fertilization), the monochorionic–diamniotic pairs (intermediate, splitting between the fourth and the seventh day post-fertilization), and the monochorionic–monoamniotic pairs (late, splitting after the eighth day post-fertilization).

What data is collected?


Pregnancy: mode of conception, information about the pregnancy itself such as gravidity, parity, gestational age, chorionicity, amnionicity, etc.

Mother: pathologies during the pregnancy


Delivery: mode of delivery, presentation at birth, time of birth, amnion, etc.

Neonate: measurements of the neonates, the presence of congenital malformations, etc.

Placenta and umbilical cord: The placenta’s are examined by trained midwifes as close as possible to birth. Measurements of the placenta and umbilical cord are taken, the shape of the placenta, number of membranes and zygosity are determined.

Biological sample: A biopsy of the placenta per child is taken at the end of the placenta examination. Every biopsy is taken as close as possible to the umbilical cord insertion. The biopsies are saved at -80°C for future scientific research.