Objective
Uncontrolled studies suggest that in vitro fertilization twins have increased rates
of preterm birth and low birth weight and would warrant increased antenatal monitoring.
The objective of this meta-analysis was to determine whether the incidence of poor
obstetric outcomes is higher for in vitro fertilization twins than for spontaneously
conceived twins who were matched for maternal age.
Study design
Medline and EMBASE were searched with comprehensive search strategies. Case-control
and cohort studies of twins who were conceived by in vitro fertilization or in vitro
fertilization/intracytoplasmic sperm injection, with the transfer of fresh embryos
or cryopreserved (frozen) in women with infertility, and/or whose partners were subfertile
or infertile, compared with naturally (spontaneously) conceived twins who were matched
for maternal age (case-control studies) or which were controlled for it (cohort studies).
Two reviewers independently assessed titles, abstracts, and study quality and extracted
the data. Statistical analysis was performed with commercial statistical software.
Dichotomous data were meta-analyzed with odds ratios as measures of effect size, and
continuous data was meta-analyzed with mean differences. Interstudy variation was
incorporated with the assumption of a random effects model for the treatment effect.
Results
Compared with spontaneously conceived twins who were matched for maternal age, in
vitro fertilization twins have an increased risk of preterm birth between 32 and 36
weeks of gestation (odds ratio, 1.48; 95% CI, 1.05-2.10), and an elevated risk of
preterm birth at <37 weeks of gestation when parity is also matched for an odds ratio
of 1.57 (95% CI, 1.01-2.44). There was an increased rate of cesarean delivery among
in vitro fertilization twins (odds ratio, 1.33; 95% CI, 1.06-1.67). There were no
significant differences in incidences of perinatal death, low birth weight infants,
or congenital malformations.
Conclusion
In vitro fertilization twins have increased rates of preterm birth compared with spontaneously
conceived twins who were matched for maternal age, despite the fact that their outcomes
would be expected to be better because of the decreased proportion of monochorionic
twins.
Key words
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Article Info
Publication History
Accepted:
November 29,
2004
Received in revised form:
November 16,
2004
Received:
August 16,
2004
Identification
Copyright
© 2005 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
