查了一下才知道,原来12周就有这么高的准确率。
Ultrasound Obstet Gynecol. 1999 May;13(5):305-7.
First-trimester determination of fetal gender by ultrasound.
Efrat Z, Akinfenwa OO, Nicolaides KH.
Harris Birthright Research Centre for Fetal Medicine, King's College
Hospital Medical School, London, UK.
Comment in:
* Ultrasound Obstet Gynecol. 1999 May;13(5):299-300.
* Ultrasound Obstet Gynecol. 2000 Mar;15(3):262-3.
Abstract
OBJECTIVE: To assess the accuracy of fetal sex determination at 11-14 weeks
of gestation.
METHODS: Fetal gender assessment by ultrasound was prospectively carried out
in 172 singleton pregnancies at 11-14 weeks of gestation immediately before
chorionic villus sampling for karyotyping. The genital region was examined
in a midsagittal plane and the fetal gender was assigned as male if the
angle of the genital tubercle to a horizontal line through the lumbosacral
skin surface was greater than 30 degrees and female when the genital
tubercle was parallel or convergent (less than 30 degrees) to the horizontal
line.
RESULTS: The accuracy of sex determination increased with gestation from 70.
3% at 11 weeks, to 98.7% at 12 weeks and 100% at 13 weeks. In the male
fetuses, there was a significant increase in the angle of the genital
tubercle from the horizontal with crown-rump length. Male fetuses were
wrongly assigned as female in 56% of cases at 11 weeks, 3% at 12 weeks and 0
% at 13 weeks. In contrast, only 5% of the female fetuses at 11 weeks were
incorrectly assigned as male and this false-positive rate was 0% at 12 and
13 weeks.
CONCLUSION: The clinical value of determination of fetal sex by ultrasound
is in deciding whether to carry out prenatal invasive testing in pregnancies
at risk of sex-linked genetic abnormalities, because invasive testing would
be necessary only in pregnancies with male fetuses. Our results suggest
that a final decision on invasive testing for sex-linked conditions should
be undertaken only after 12 weeks of gestation.
PMID: 10380292 [PubMed - indexed for MEDLINE]