Re: Baby measuring small for dates

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• In reply to: Melinda: "Baby measuring small for dates"

Ultrasound measurements have an error in the technique. It would be normal practice NOT to challenge the dates if the USS measurements were less than 2 weeks different from the menstrual dates. At 18-22 weeks a normal measurement of the head or thigh bone is accurate for dating to about plus or minus 2 weeks. A baby length (CRL)at 12 weeks is accurate to about +/- 10 days. After 24 weeks measurements are +/- FOUR weeks.

So the later the scan the less accurate the scan dates are. Certainly in my practice we would not change dates unless two scans before 22 weeks show a greater than 2 week difference from the menstrual dates.

On the conception issue .... remember that conception does not equal intercourse or vice versa! The egg hangs around for about 24 hours but sperm can hang around longer. Timing of egg production is therefore useful (but not definite) but timing of sex isn't when it comes to dating a pregnancy.

On the issue of chromosome abnormalities don't worry ....get some more accurate info ....see an Obstetrician and I'm sure they will reassure you.

--
Ross Welch
Consultant in Fetomaternal medicine
Duchess of Westminster Wing
Arrowe Park Hospital
Upton, Wirral.
UK

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• In reply to: Melinda: "Baby measuring small for dates"