Live-birth rates and multiple-birth risk using in vitro fertilization.
BACKGROUND
To maximize birth rates, physicians who perform in vitro fertilization (IVF) often transfer multiple embryos, but this increases the multiple-birth risk. Live-birth and multiple-birth rates may vary by patient age and embryo quality. One marker for embryo quality is cryopreservation of extra embryos (if embryos are set aside for cryopreservation, higher quality embryos may have been available for transfer).


OBJECTIVE
To examine associations between the number of embryos transferred during IVF and live-birth and multiple-birth rates stratified by maternal age and whether extra embryos were available (ie, extra embryos cryopreserved).


METHODS
Retrospective cohort of 300 US clinics reporting IVF transfer procedures to the Centers for Disease Control and Prevention in 1996.


METHODS
A total of 35554 IVF transfer procedures.


METHODS
Live-birth and multiple-birth rates (percentage of live births that were multiple).


RESULTS
A total number of 9873 live births were reported (multiple births from 1 pregnancy were counted as 1 live birth). The number of embryos needed to achieve maximum live- birth rates varied by age and whether extra embryos were cryopreserved. Among women 20 to 29 years and 30 to 34 years of age, maximum live-birth rates (43 % and 36%, respectively) were achieved when 2 embryos were transferred and extra embryos were cryopreserved. Among women 35 years of age and older, live-birth rates were lower overall and regardless of whether embryos were cryopreserved, live-birth rates increased if more than 2 embryos were transferred. Multiple-birth rates varied by age and the number of embryos transferred, but not by whether embryos were cryopreserved. With 2 embryos transferred, multiple-birth rates were 22.7%, 19.7%, 11.6%, and 10.8% for women aged 20 to 29, 30 to 34, 35 to 39, and 40 to 44 years, respectively. Multiple-birth rates increased as high as 45.7% for women aged 20 to 29 years and 39.8% for women aged 30 to 34 years if 3 embryos were transferred. Among women aged 35 to 39 years, the multiple-birth rate was 29.4% if 3 embryos were transferred. Among women 40 to 44 years of age, the multiple-birth rate was less than 25% even if 5 embryos were transferred.


CONCLUSIONS
Based on these data, the risk of multiple births from IVF varies by maternal age and number of embryos transferred. Embryo quality was not related to multiple birth risk but was associated with increased live-birth rates when fewer embryos were transferred.
Schieve
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LA
Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, GA 30341, USA. LJS9@cdc.gov
Peterson
H B
HB
Meikle
S F
SF
Jeng
G
G
Danel
I
I
Burnett
N M
NM
Wilcox
L S
LS
D000328:Adult; D001723:Birth Rate; D015925:Cryopreservation; D004624:Embryo Transfer; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D038622:Internationality; D008423:Maternal Age; D009099:Multiple Birth Offspring; D011247:Pregnancy; D011256:Pregnancy Outcome; D011272:Pregnancy, Multiple; D012189:Retrospective Studies; D012306:Risk