© 2017, GENASSIST, Inc. 

By Keith S. Wexler, MBA, Maternal Fetal and Prenatal Diagnosis and Biotech/Life Sciences Consultant, GENASSIST, Inc.

Paul Wexler, M.D., F.A.C.O.G., Medical Director, GENASSIST, Inc.

Clinical Professor, Department of OB/GYN, University of Colorado Health Sciences Center

Clinical Professor, Division of Genetics/Dept. of Pediatrics, Univ. of Colorado/The Children’s Hospital

Background: We are getting more and more referrals to perform an ultrasound for possible Post Dates Pregnancy (after 40 weeks gestation from First Day of Last Menstrual Period (LMP)with or without Intrauterine Growth Restriction (IUGR) as an indication.

Some of these patients have chosen against any ultrasound studies in pregnancy due to the patient’s fear of “exposing” her baby to ultrasonic sound waves in pregnancy.

Without early ultrasounds used for dating these requests are difficult.

It is possible to perform a Biophysical Profile including:

  • Fetal measurement to estimate fetal size and “calculated” gestational dates
  • Evaluate fetal and placental position
  • Amniotic fluid measurements
  • Evaluate fetal movement and tone
  • Evaluate fetal respirations
  • Cord and placental Doppler flow patterns
  • Non stress testing is often added after 42 weeks gestation or if fetal well-being is a concern

*Estimation of fetal weight and gestational age is more problematic.

Estimate of fetal weight late in gestation is often reported as +/- 400-500 grams and gestational age is often a guess.

Small infants may appear to be less than gestational age and large infants may appear greater than their actual gestational age.

The recent *Practice Bulletin Summary in the Journal of Obstetrics and Gynecology Volume 28, Number 6, December 2016 on Ultrasound in Pregnancy set forth Clinical Management for Obstetricians an-Gynecologists pp 1459-60. Among the recommendations “for all pregnant patients” are included:

At various gestational ages, ultrasound examination is an accurate method of determining: gestational age, fetal number, viability and placental location.

  • *“Gestational age is most accurately determined in the first half of pregnancy”
  • *”Umbilical Doppler velocimetry used in conjunction with standard fetal surveillance such as non-stress tests, biophysical profiles or both is associated with improved outcomes in fetuses with fetal growth restriction”

Analysis: Even with the recognition that most children are going to be healthy and parents always wish to anticipate such an outcome in their child, it probably is appropriate to share the above information with the expectant parents so that a child at some increased risk has the best chance for a positive outcome.

For patients that have had No Dating Ultrasounds earlier in pregnancy, an ultrasound performed after 40 weeks gestation can only attempt to assess fetal well-being at that particular point in time. It cannot establish the gestational age of the pregnancy.