Updated November 2014 Judith Bliss, MD

CCRMC OBGYN Prenatal Guideline
Consultation available 24 hours per day from OB on-call at 925-370-5608 or via page/amion, via inbasket to OB dept member or by calling Perinatologist at 510-444-0790 during the day and 510-204-1572 after hours. Consultation appointments or transfer of care to more experienced prenatal clinician available at major clinics sites—see consultation guidelines for more information.

Prenatal Fetal Evaluation Options

All patients are offered the California State Screen consisting of a first trimester blood test 10w-13w6d, a nuchal translucency ultrasound at 11w-14w (if apt available) and a second trimester blood test from 15w-20w. Women older than 35 at EDD or with additional risk factors may opt directly for diagnostic tests such as amniocentesis. Cell free fetal DNA is generally available to our patients if the state screen is positive or they have other risk factors through the Perinatology referral sites--East Bay Perinatal Medical Associates and Diablo Valley Perinatology. Level II anatomy ultrasounds are recommended for women over 35y/o, monochorionic twin gestations, pregestational DM, or history of prior fetus with possibly recurrent genetic abnormality.

Screening Tests
  • Screening: 1st and 2nd tri blood testing, NT ultrasound.
    • Result is a statistical ratio of risk (<1:250 risk for Down’s syndrome is considered “screen negative”)
    • State law requires screening to be offered to all patients but it is not a required or recommended part of prenatal care. It is optional.
    • In contrast,CVS and amniocentesis: give yes or no answer with very high predictive value

Screening options:
  • Quad screen (Second Trimester State Screen Only):
1 blood draw (HCG, E3, inhibin A and AFP) at 15-20 wks
80% sensitivity for Down’s, 5% false positive
  • Serum Integrated screening (First and Second Trimester State Screen without NT ultrasound): blood draw at 10-13w6d (HCG and PAPP-A) and 2nd blood draw –quad screen
85 % sensitivity for Down’s, 5% False positive
  • Fully integrated screening (First and Second Trimester State Screen with NT ultrasound: 1st tri blood draw, 2nd tri quad screen and NT ultrasound (11-14 wks)
90% sensitivity, 2-5% false positive
  • Combined Screen (First Trimester State Screen and NT Ultrasound, without Second Trimester State Screen): 1st tri blood draw (HCG and PAPP-A) at 10-13w6d and NT ultrasound at 11-14w
85% sensitivity, 5% False positive
  • If the patient get their 1st tri blood test (in our lab with the 1st tri screen form) the week before their NT sono, the perinatologist will give them their combined screen result that day.
  • If they get their blood draw later, you must call the state screening office (number on bottom of state screening form) to obtain the result. The NT and blood test results are not automatically linked and there is no result. State screening result forms are loaded into media.

  • Cell Free DNA – maternal blood draw at 10+ wks (harmony, maternitT21, panorama, verify)
99% sensitive for down’s, <0.1% false positive
Less sensitive for trisomy 18,13 and does not test at all for many other anomalies and syndromes. The test is still evolving quickly. Some brands are adding X/Y analysis to identify X-linked conditions but not all. May be inaccurate in disappearing twins or if placental mosaicism.

  • WHY: Advantage – non invasive but highly sensitive for down’s
Disadvantage – Much narrower scope (mostly for down’s) compared to CVS/Amnio (full karyotype) and other screening tests (wide range of syndromes)
  • WHO: Covered by CCHP for any patient who requests it.
Covered by medi-cal for a positive screening test (any of items 1-4 above), AMA (35+ at time of delivery), other high risk condition (prior fetal anomaly, balanced translocation in 1 patient etc).
  • HOW: Usually ordered after genetic counseling by the perinatology office (East bay perinatal or Diablo valley perinatal). You make the referral for genetic counseling on the paper referral form and they do the rest. There is no order in epic for the referral or blood test.
  • If the patient has an abnormal NT or combined screen result, the perinatologist may offer either cell-free DNA or CVS that same day so the patient already has a plan by the time you find out.

Diagnostic Testing:
  • CVS
10-14 wks
Transcervical or transabdominal depending on placental location
Loss rate very difficult to assess: Best guess 1:350 (range 1:100 to 1:1600)
Provider skill important
Remember to order the 15-20 wk quad screen for the AFP result. CVS does not test for neural tube defects.
  • Amniocentesis - 15+ wks
Widely available
Loss rate difficult to assess: Best guess 1: 350 (range 1:300 to 1:1000)
  • These tests covered by CCHP for any patient who requests it. Covered by medi-cal for a positive screening test (any of items 1-5 above), AMA (35+ at time of delivery), other high risk condition (prior fetal anomaly, etc).
  • If patient chooses a diagnostic test, do not also order an NT sono or it will not be covered.
  • Refer to East Bay perinatal (Oakland) or Diablo Valley (Walnut Creek) on paper referral form.

Who might benefit from Antepartum Testing with Biweekly NST and Weekly AFI starting at 32 weeks for abnormal State Screen ?

Results for each serum analyte marker tested are reported in MoM (multiples of the mean).
We recommend starting antenatal testing (biweekly NST and weekly AFI) at 32 weeks for the abnormal values listed in Table 1.

Table 1: Abnormal Serum Analyte Values that Warrant Antenatal Testing @ 32 wks

PAPP-A <0.29 MoM
AFP >2.5 MoM
BhCG >4.0 MoM
Inhibin >4.0 MoM
BhCG + Inhibin BOTH >2.0 MoM
In contrast, an elevated risk on one of the screening panels reported on the BACK of the form (Down’s, Trisomy 18, Open neural tube defects or SLOS) does NOT necessarily mean your patient needs biweekly NSTs and weekly AFIs. Most of the patients who screen positive on one of these panels are not carrying abnormal fetuses and if the level II ultrasound and possible amniocentesis are normal they do not need additional evaluation. Antenatal testing IS indicated in cases of Down syndrome confirmed on CVS or amniocentesis.