Biparietal diameter
Abbreviation: BPD
Biparietal diameter (BPD) is an ultrasound measurement taken across the widest part of your baby's skull, from one side of the head to the other. It is one of the key measurements used to estimate gestational age in early pregnancy and to monitor fetal growth as pregnancy progresses. BPD is measured in millimetres and plotted against standard growth charts. A result that falls outside the normal range does not automatically indicate a problem, as head shape, fetal position, and ethnic variation all affect the reading. Your obstetrician will always interpret BPD alongside other measurements before drawing any conclusions.
What This Means for You
Understanding Biparietal diameter is an important part of your second/third trimester journey. During pregnancy, your care team will use this term regularly. Being familiar with it means you can ask better questions and feel more confident at your antenatal appointments.
Explore our Pregnancy hubGood to Know
BPD is less reliable for dating a pregnancy after 28 weeks, as natural variation in head size increases. Earlier first or second trimester scans give more accurate gestational age estimates.
Source: https://www.acog.org/womens-health/faqs/how-your-fetus-grows-during-pregnancy
Always consult your healthcare provider for personalised advice.
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