Prenatal Screening Tests
Routine Lab testing in prenatal care:
1st Trimester (1 - 14 weeks):
CBC: anemia = Hb <10 g/dL (normal 10 - 12).
▼ MCV and other RBC indices low, and ▲ RDW. Iron deficiency most common cause. Give iron. Test thalassemia if anemia does not improve.
▼ Hb, ▲ MCV, ▲ RDW: Give folate
WBC >16,000/mm3 is abnormal
Thrombocytopenia (<150,000/mm3): Correlate clinically with ITP or HELLP syndrome.
Blood type, Rh and Ab screen (direct and indirect Coombs for AAT)
Rh negative mothers may become sensitized (anti-D Ab) → risk of erythrobalstosis fetalis in the next pregnancy.
Give RhoGAM at 28 weeks after first screening for absence of anti-D abs (DAT).
Indirect Coombs test for atypical antibody (AAT) detects atypical RBC Ab's.
Genitourinary screening
Cervical PAP smear: Detects cervical dysplasia or malignancy. Refer to Gyn for management.
UA and urine culture: Screen underlying UTI. Screen for asymptomatic bacteriuria (ASB)
Always treat ASB in pregnancy to prevent pyelonephritis (30% risk if untreated). Rx: Nitrofurantoin, cephalosporins, amoxicillin
Immunization Status
Rubella ab. if negative Rubella IgG, it means mother is at increased risk of primary rubella infection.
Do not give rubella immunization in pregnancy. Immunize seronegative patient after delivery.
HbsAg. If positive indicates risk for vertical transmission of HBV.
Order HBeAg. If positive, indicates highly infectious state.
Infectious syphilis: VDRL or RPR
Confirm positive VDRL/RPR with MHATP or FTA-ABs. If positive treat with PCN IM. PCN allergic, desensitize and then treat with PCN.
HIV (ELISA). Confirm ELISA with Western blot test (presence of HIV core and envelope antigen).
Always get consent for HIV testing. Not needed now.
All babies born to HIV +ve mothers will have HIV ab +ve due to passive transport of maternal Abs. +ve Abs in infants do not necessarily mean infection in infant.
Antiretrovirals are not C/I in pregnancy.
Cervical culture for Gonorrhea, Chlamydia and Trichomonas.
Gram stain, G & C, Trichomonas vaginalis (can cause premature labor).
Tx: Azithromycin PO and Ceftriaxone IM. Alteranative, Amoxicillin PO.
Bacterial vaginitis/vagniosis: Metronidazole, PO or clindamycin PO
Optional tests:
PPD. Test for exposure to TB in high risk mothers. +ve test is induration, not erythema.
Negative PPD: no further follow-up is needed.
Positive PPD: CXR to rule out active disease.
Treat +ve PPD /-ve CXR: INH and B6 for 9 months.
+ve PPD / +ve CXR / +ve sputum: Triple therapy anti-TB. Avoid streptomycin in pregnancy because of the risk of ototoxicity in the fetus.
Trisomy testing (ß-HCG, PAPP-A - pregnancy associated plasma protein A; fetal nuchal translucency at 10 wks), offered to high-risk pregnancies (females >35 at delivery, women with a history of prior trisomy 21)
+ve screening test is confirmed with CVS in 1st trimester.
2nd Trimester (14 - 26 weeks):
1 hr 50 gm OGTT given between 24 – 28 wks. No fasting needed.
Abnormal result: BS >140 mg/dL. Do 3 h, OGTT. Needs fasting ON.
Anemia
CBC measured between 24 - 28 weeks. Hb <10 g/dL = anemia. Iron deficiency is the most common cause, even if not present in 1st trimester.
Give Iron supplementation.
Atypical antibodies:
Indirect Coombs test performed in Rh-negative women to look for atypical anti-D-Ab before giving RhoGAM.
RhoGAM is not indicated in Rh negative women who have developed anti-D antibodies.
GBS screening (vaginal and rectal culture) at 35 – 37 weeks.
+ve GBS culture is a high risk for sepsis in newborn.
Presumptive treatment based on certain risk factors for neonatal infections, including preterm labor, preterm premature rupture of membrances (P PROM), prolonged rupture of membranes, intrapartum fever, and a previous neonate with GBS infection.
Treat with intrapartum IV ABx. PCN G IV, clindamycin IV or eyrthromycin in PCN allergic patients.
Optional tests:
Quadruple marker screen (MSFAP, ß-HCG, estriol, add dimeric inhibin-A in high risk women)
16 - 20 weeks gestation.
MS-AFP is measured in multiple of the median (MoM). It increases with gestational age.
> 2.2 MoM is considered elevated.
< 2.5 MoM is considered normal.
Inhibin A is made by the placenta during pregancy and normally remains constant during 15 - 18 week of pregnancy. The level of inhibin A is increased in the blood of mothers of fetuses with Down syndrome.
▲ MS-AFP: NTD, ventral wall defect, twin pregnancy, placental bleeding, sacrococcygeal teratoma.
Abnormal MS-AFP, perform US to confirm dating of pregnancy. If dating error, repeat MS-AFP. Normal repeat MS-AFP is reassuring. If repeat MS-AFP is elevated, do US.
If MS-AFP > 7 MoM and family history of NTDs: do TVUS
If ▲ MS-AFP: do amniocentesis for amniotic fluid AF-AFP level and acetylcholinesterase activity. Elevated levels of amniotic fluid-acetycholinesterase activtiy is specific to open NTD.
For ▼ MS-AFP: amniocentesis for karyotyping.
▼ MS-AFP: Trisomy 21, Trisomy 18
Trisomy 21 (Down syndrome): ▼ MS-AFP, ▼ Estriol, ▲ Beta-hCG, ▲ Inhibin-A
Trisomy 18 (Edward syndrome): ▼ MS-AFP, ▼ Estriol, ▼ Beta-hCG.
Parameters routinely measured on subsequent visits:
BP, wt., ut. fundal ht., fht, fetal presentation and activity, urine glucose and protein.
Anemia Hb <10 g/dL.
Scuba diving in pregnancy increases the risk of decompression injury and gas emboli in fetus
In hypothyroidism pregnancy check TSH every trimester.