Trends in dizygotic twins by state in the U. S. from 1990 to 2001

Abstract

JAMES EGAN, PETER BENN, LUCYBETH NIEVES, LILLIAN KAMINSKY, JEFFREY SPENCER, ADAM BORGIDA, University of Connecticut, Obstetrics and Gynecology, Farmington, Connecticut, University of Connecticut, Pediatrics, Farmington, Connecticut, University of Medicine and Dentistry of New Jersey, Maternal-Fetal Medicine, New Brunswick, New Jersey, Hartford Hospital, Obstetrics and Gynecology, Hartford, Connecticut OBJECTIVE: An increase inDZ twinning is amarker for assisted reproductive technology (ART). We estimated the livebirth (LB) prevalence of monozygotic (MZ) and dizygotic (DZ) twins by state in the U. S. from 1990 to 2001. STUDY DESIGN: Using data from NCHS, we determined the numbers of MM, FF and MF twin pairs for the US for each year from 1990 to 2001 by state. Birth certificate data were matched on the basis of twin records with the same city, state, year and month of birth, maternal race, maternal age and paternal age. All MF pairs were considered DZ. For DZ twins, the ratios of MM/MF and FF/MF were calculated based on ratios from 5,044 twin pairs in the East Flanders Prospective Twin Survey (Loos et al, Twin Res. 1998;1:167). Using these ratios we calculated the number of DZ MM and FF twins. Total DZ twins equals unlike sex plus like sex DZ twins. The MZ twins were estimated by subtracting the total number of DZ twins from all twins. We estimated MZ and DZ twins by state. RESULTS: There were 47,995,361 livebirths (LB) between 1990 and 2001 in the US of which 1,245,220 (2.6%) were twins. Overall, DZ twins increased from 8.0/1,000 deliveries to 9.7/1,000 deliveries. The birth prevalence of DZ twins in the 4 highest and 4 lowest states for each time period is seen in Table 1. CONCLUSION: DZ twin pairs were highest in MA and CT and ID, NM and HA were lowest in both time periods. This suggests a strong presence of ART in states with high rates of DZ twins.