© 2018, GENASSIST, Inc.

By Keith S. Wexler, MBA, Maternal Fetal Medicine, 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 receiving increased requests from patients for ultrasound evaluation of placental position relative to a prior low segment transverse Cesarian scar in anticipation of the probable success of a planned Vaginal Birth After Cesarian delivery (VBAC).

Analysis: Although there are “guidelines” from the American College of OB/GYN and the Royal College of Obstetricians and Gynecologists and opinion pieces from individual practitioners and birth centers, clear recommendations for patient selection, clinical and laboratory (specifically ultrasound) evaluation and management during the pregnancy and in labor are sparse and often incomplete.

More recently, patient requests for Trial Of Labor After Prior Cesarian Delivery (TOLAC) are increasing after a period of more aggressive recommendations for Elective Repeat Cesarian (ERC) based upon a suspected lower risk for the mother and baby.

Some studies suggest a VBAC success rate of:

  • 87% if only one prior C-Section and no relative contraindication
  • 90% if there was a vaginal delivery prior to the C-Section
  • 96% if there was a previous successful VBAC

Relative contraindications for Trial of Labor After Cesarian (TOLAC) have included:

  • Suspected large baby
  • Post dates
  • Malpresentation
  • Multiple gestations
  • Prior classical uterine scar
  • Multiple prior cesarian deliveries especially with no prior vaginal births
  • Maternal obesity
  • Advanced maternal age (greater than 40 years)
  • Low Bishop Score (assignment of points to the cervix and pelvis to evaluate the readiness of the cervix for labor induction and the likelihood of vaginal delivery).
  • Decreased lower uterine segment uterine thickness (less than 2 mm) evaluated transabdominally or transvaginally (possibly more reliable) or both.

Are there reasonable recommendations for the use of ultrasound in pregnancy to identify patients that may have a decreased likelihood of success for a vaginal birth after prior cesarain delivery?

We might recommend the following for patients to consider:

    • An early ultrasound after 6 weeks gestation, to help confirm gestational dates
    • First Trimester Aneuploidy Screening between 11 and 14 weeks gestation, to estimate risk for a fetus with a chromosomal evaluation or heart defect and perform a limited evaluation of the fetal number, viability and structural integrity of the fetus and organ development.
    • A Level II ultrasound study at 18-22 weeks gestation, to perform a more complete fetal anatomical evaluation, placental localization and evaluation of the cervix and confirmation of gestational dates.
    • Follow-up ultrasound evaluation after 31-35 weeks gestation (realizing the limitations of ultrasound); evaluation of fetal size, fetal presentation, placenta localization especially in relationship to probable cesarian scar, amniotic fluid measurements, fetal biophysical evaluation, placental and cord Doppler evaluation and measurements of the lower uterine segment, evaluation of possible presence of low lying placenta, placenta previa and likelihood of 1placenta accreta, 2placenta increta or 3placenta percreta.

1Placenta Accreta – growth of portions of the placenta and placental blood vessels into the uterus which makes placental removal difficult with increased risk for bleeding.

2Placenta Increta – attachment of the placenta to the muscles of the uterus.

3Placenta Percreta – growth of the placenta through the uterine wall, sometimes attaching to the neighboring organs e.g. bladder, bowel etc.)