Does assisted hatching pose a risk for monozygotic twinning in pregnancies conceived through in vitro fertilization?
OBJECTIVE
To examine the association between assisted hatching and monozygotic (MZ) twinning.


METHODS
Case-control.


METHODS
Population-based sample of IVF-ET cycles initiated in U.S. clinics, 1996.


METHODS
The IVF-ET (n = 35,503) cycles and 11,247 resultant pregnancies.


METHODS
Use of an assisted hatching procedure on embryos transferred.


METHODS
Cases were pregnancies for which number of fetal hearts observed on ultrasound exceeded number of embryos transferred. These pregnancies were considered to contain at least one MZ set of twins. Cases were compared with two control groups: other multiple-gestation pregnancies (>/=2 fetal hearts but number of fetal hearts </= number of embryos transferred); and singleton pregnancies (1 fetal heart).


RESULTS
Women with a case pregnancy were more likely to have received embryos treated with assisted hatching procedures than were women in either control group. After adjustment for patient age, number of embryos transferred, prior cycles, infertility diagnosis, intracytoplasmic sperm injection, and whether embryos from the current cycle were cryopreserved for later use, odds ratios and 95% CIs for use of assisted hatching were 3.2 (1.2-8.0), compared with other multiple-gestation pregnancies, and 3.8 (1.8-9.8), compared with singleton pregnancies.


CONCLUSIONS
Assisted hatching may pose a risk for MZ twinning.
Schieve
L A
LA
Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, Georgia 30341, USA. LSJ9@cdc.gov
Meikle
S F
SF
Peterson
H B
HB
Jeng
G
G
Burnett
N M
NM
Wilcox
L S
LS
D000328:Adult; D016022:Case-Control Studies; D004622:Embryo, Mammalian / Q000502:physiology; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods* / Q000706:statistics & numerical data; D006801:Humans; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000706:statistics & numerical data*; D014430:Twins, Monozygotic