Placental thickness in the second trimester: a pilot study to determine the normal range.
OBJECTIVE
We sought to determine the normal sonographically measured placental thickness in millimeters at the second-trimester scan (18 weeks to 22 weeks 6 days) and determine whether the measurement should be adjusted for gestational age and the placental site.


METHODS
We conducted a cross-sectional observational pilot study involving 114 consecutive patients with singleton pregnancies presenting for routine second-trimester sonography between 18 weeks and 22 weeks 6 days.


RESULTS
The unadjusted overall mean placental thickness was 24.6 (SD, 7.29) mm. The placental thickness was normally distributed. On multivariable analysis, the predicted mean thickness was 6.6 mm (95% confidence interval, 4.4 to 8.8 mm; P < .001) less in anterior compared to posterior or fundal placentas and increased by 0.6 mm (95% confidence interval, -0.5 to 1.7 mm; P = .27) for each week increase in gestation after 18 weeks


CONCLUSIONS
The placental position and possibly gestational age need to be considered when determining placental thickness. Anterior placentas are approximately 7 mm thinner than posterior or fundal placentas. Anterior placentas of greater than 33 mm and posterior placentas of greater than 40 mm should be considered abnormally thick.
Royal Women's Hospital, Flemington Road, Parkville, VIC 3052, Australia. anna.lee.email@gmail.com
Anna J
AJ
Lee
Michael
M
Bethune
Richard J
RJ
Hiscock
D000293:Adolescent; D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D010865:Pilot Projects; D010920:Placenta / Q000000981:diagnostic imaging*; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D012016:Reference Values; D016216:Ultrasonography, Prenatal / Q000379:methods*