BACKGROUND
Although the smaller twin's crown-rump length is most accurate in establishing the
estimated due date in dichorionic gestations, societal guidelines favor the use of
the larger twin measurements based on concern for missing a diagnosis of fetal growth
restriction.
OBJECTIVE
This study aimed to compare the accuracy of the diagnosis of early- and late-onset
fetal growth restriction in dichorionic twin gestations conceived by assisted reproductive
technology using the estimated due date as established by the crown-rump length of
the smaller vs larger twin.
STUDY DESIGN
This was a 10-year retrospective cohort study of nonanomalous, dichorionic gestations
conceived with assisted reproductive technology at 2 institutions. The incidence of
early-onset (<32 weeks of gestation) and late-onset (≥32 weeks of gestation) growth
restriction derived from the Hadlock formula using the smaller and larger crown-rump
length estimated due date was compared with the true estimated due date by assisted
reproductive technology. Statistical significance was determined using the Fisher
exact test. The incidence of missed fetal growth restriction cases, false-positive
rate, and error were calculated along with the relative risk for a missed diagnosis
using the smaller crown-rump length.
RESULTS
A total of 176 subjects were screened: 81 had a fetal growth ultrasound at 24 to <32
weeks of gestation, and 58 had a fetal growth ultrasound at ≥32 weeks of gestation.
There was a significant difference in the incidence of fetal growth restriction using
the 3 dating strategies in both gestational age ranges (P<.001) with the smaller crown-rump length estimated due date more closely approximating
the true rate. Before 32 weeks of gestation, the smaller crown-rump length estimated
due date missed 2.5% of fetal growth restriction cases, whereas the larger crown-rump
length estimated due date missed 0.6% of fetal growth restriction cases, with false-positive
and error rates of 1.2% and 3.7% and 5.5% and 6.2%, respectively. After 32 weeks of
gestation, the smaller crown-rump length estimated due date missed 1.8% of cases,
whereas the larger crown-rump length estimated due date missed 0% of cases, with false-positive
and error rates of 2.6% and 4.4% and 5.3% and 5.3%, respectively. The relative risk
for a missed diagnosis of fetal growth restriction using the smaller crown-rump length
estimated due date was 1.77 for early-onset growth restriction and 1.22 for late-onset
growth restriction.
CONCLUSION
Using the estimated due date derived from the smaller twin led to a more accurate
detection of fetal growth restriction at a cost of a higher missed diagnosis rate.
Key words
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Article info
Publication history
Published online: January 18, 2023
Accepted:
January 14,
2023
Received in revised form:
January 10,
2023
Received:
October 5,
2022
Footnotes
The authors report no conflict of interest.
The views expressed in this manuscript reflect the results of research conducted by the authors and do not necessarily reflect the official policy or position of the Uniformed Services University of the Health Sciences, the Department of the Navy, the Department of the Air Force, the Department of Defense, or the US government.
T.H.D., S.K.S., M.A.S., and A.S.T. are military service members. This work was prepared as part of their official duties. Title 17 U.S.C. 105 provides that “[c]opyright protection under this title is not available for any work of the [US] [g]overnment.” Title 17 U.S.C. 101 defines a US government work as a work prepared by a military service member or employee of the US government as part of that person's official duties.
The study protocol was approved by the Naval Medical Center Portsmouth and Naval Medical Center San Diego Institutional Review Boards (IRBs) in compliance with all applicable Federal regulations governing the protection of human subjects.
Research data were derived from an approved Naval Medical Center Portsmouth, VA, IRB, protocol.
This study received no external funding.
Cite this article as: DeYoung TH, Stortz SK, Riffenburgh RH, et al. Is bigger better? A comparison of growth restriction rates using the due date derived from the smaller vs larger twin crown-rump length. Am J Obstet Gynecol MFM 2023;XX:x.ex–x.ex.
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Published by Elsevier Inc.
