Infertility, infertility treatment and twinning: the Danish National Birth Cohort

Hum Reprod. 2007 Apr;22(4):1086-90. doi: 10.1093/humrep/del495. Epub 2007 Jan 4.

Abstract

Background: We have previously observed that an increasing time to pregnancy (TTP) is associated with a reduced frequency of twin deliveries in couples not receiving infertility treatment. By using updated information, we assessed the frequencies of dizygotic (DZ) and monozygotic (MZ) twin deliveries as a function of infertility (TTP > 12 months), as well as infertility treatment.

Methods: From the Danish National Birth Cohort (1997-2003), we identified 51 730 fertile couples with TTP <or= 12 months, 5838 infertile couples who conceived naturally with TTP > 12 months and 5163 infertile couples who conceived after treatment. Information on zygosity, available for part of the cohort (1997-2000), was based on standardized questions on the similarities between the twins at the age of 3-5 years.

Results: Compared with fertile couples, the frequency of DZ twin deliveries was lower for infertile couples conceiving naturally (odds ratio 0.4, 95% confidence interval 0.2-0.7) and was much higher for infertile couples conceiving after treatment (17.3, 14.4-20.7). The frequency of DZ twin deliveries decreased with TTP in untreated couples, whereas the frequency of MZ twin deliveries remained constant.

Conclusions: The frequency of DZ twin deliveries decreased with TTP and substantially increased with infertility treatment, whereas MZ twin deliveries remained substantially unchanged.

Publication types

  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Cohort Studies
  • Denmark
  • Female
  • Fertility
  • Humans
  • Infertility / therapy*
  • Male
  • Odds Ratio
  • Ovulation
  • Pregnancy
  • Pregnancy Outcome
  • Pregnancy, Multiple
  • Twins, Dizygotic*
  • Twins, Monozygotic*