Risk factors for SGA fetus /neonate

Risk factors for SGA fetus /neonate بسم الله الرحمن الرحیم

Methods of screening for the SGA fetus/neonate include: • In the 1 and 2 trimesters: • Medical and obstetric history and examination • Maternal serum screening • Uterine artery Doppler • In the 2 and 3 trimester : • Abdominal palpation and measurement or symphysisfundal height (SFH)

History

All women should be assessed at booking for risk factors for a SGA fetus / neonate to identify those who require increased surveillance.

Women who have a major risk factor (OR>2) should be referred for serial ultrasound measurement of fetal size and assessment of wellbeing with artery doppler from 26-28 weeks of pregnancy.

Women who have three or more minor risks factors should be referred for uterine artery Doppler 20-24 weeks of gestation.

Risk factors

Previous pregnancy history • Previous SGA OR: 3.9 • Previous stillbirth OR: 6.4 • Previous preeclampsia OR: 1.31 • pregnancy interval • <6 Months OR: 1.26 • > 60 months OR: 1.29

Women that have previously had a SGA neonate have at least twofold increased risk of a subsequent SGA neonate. The risk is increased further after two SGA births.

Women with a prior history of other placenta – mediated disease are also at increased risk of a subsequent SGA neonate, include: • Prior preeclampsia and prior stillbirth particular those with a history of previous preterm unexplained stillbirth due to the association with FGR.

pregnancy interval < 6 month OR: 1.26 > 60 month OR: 1.29

Maternal medical conditions • Diabetes and vascular disease OR6 • Moderate and severe renal impairment (especially with hypertension) OR 5.3 • Antiphospholipid syndrome OR 6.22 • Chronic hypertension OR  2.5 • Systemic lupus erythematosis (SlE) • Certain types of congenital heart dis. (Particular cyanotic congenital heart dis.) (there are no papers reporting OR)

Asthma • Thyroid disease • Inflammatory bowel disease • Depression

Other maternal risk factors • Maternal Age ≥ 35 years OR 1.4 • Maternal age ≥ 40 years OR  3.2 • Nulliparity OR  1.89 • Social deprivation • Body mass index • BMI<20 OR:1.2 • BMI 25-29.9 RR: 1.2 • BMI>30 OR:1.5 • Daily vigorous exercise OR:3.3 • Vaginal bleeding during the 1 trimester OR: 2.6

Continue • Maternal exposure to domestic violence during pregnancy OR: 1.53 • Low maternal weight gain • Moderate alcohol intake • Cigarette smoking (dose dependent ) • 1-10/day OR 1.54 • ≥11 /day  OR 2.21 • Drug use (most significant with cocaine) OR 3.23 • Caffeine consumption ≥ 300mg per day in the 3 trimester • Low fruit intake pre-pregnancy OR 1.9 (high green leafy vegetable intake pre-pregnancy to be protective) • IVF singleton pregnancy OR 1.6

Maternal SGA OR: 2.64 • Paternal SGA OR: 3.47

Major risk factors (OR>2) should prompt referral for serial ultrasound measurement of fetal size and assessment of wellbeing with umblical artery Doppler .

The presence of multiple minor risk factors is likely to constitute a significant risk for the birth of a SGA neonate and there is a rationale for further screening using uterine artery Doppler at 20 weeks

Current pregnancy complications /developments

Biochemical marker used for down synd. (DS) screening • Due to their placental origin, several biochemical markers have been investigated as screening tests for a SGA fetus.

Low predictive accuracy for SGA • Alpha fetoprotein (AFD) (>2.5 MoM or <0.25 MoM) • Elevated hCG (>3MoM) • Inhibin A (≥2 MoM) • Low unconjugatedEstriol (50.5 MoM) • Combined triple test

2nd trimester DS markers have limited predictive accuracy for SGA

A low level (<0.415 MoM) of the 1st trimester PAPP-A should be considered a major risk factor for delivery of a SGA neonate.

There is some evidence that addition of fetal size at 18-20 weeks of gestation or fetal growth between 11-14 and 18-20 weeks of gestation to 1st trimester serum markers improved prediction of a SGA infant.

Uterine artery Doppler • SGA birth, particularly when severe (birth weigh< 3nd centile) or necessitating <36 weeks of gestation is characterized by failure of trophoblast invasion of myometrial uterine spiral arteries and reduced utero placental blood flow.

Non-pregnant and first trimester artery blood flow velocity waveforms are associated with low end-diastolic velocities and an early diastolic notch.

Persistent nothing or abnormal flow velocity ratios after 24 weeks of gestation are associated with inadequate trophoblast invasion of the myometrial spiral arteries.

Reduced endovascular trophoblast invasion of decidual spiral arteries has been associated with same waveform abnormalities as early as 10-14 weeks of pregnancy.

Women with an abnormal uterine artery Doppler at 20-24 weeks and/or notching should be referred for serial ultrasound measurement of fetal size and assessment of wellbeing with umbilical artery Doppler at 26-28 weeks of pregnancy.

In a low risk population, uterine artery Doppler has limited accuracy to predict a SGA neonate.

In high risk populations, uterine artery Doppler at 20-24 weeks of pregnancy has a moderate predictive value for a severely SGA neonate.

Women with a normal uterine artery Doppler do not require serial measurement of fetal size and serial assessment of wellbeing with umbilical artery Doppler unless they develop specific pregnancy complications, (APH, hypertension) however, they should be offered a scan for fetal size and umbilical artery Doppler during the 3nd trimester.

Fetal echogenic bowel • Fetal echogenic bowel has been shown to be independently associated with a SGA neonate and fetal demise. • Serial measurements of fetal size and umbilical artery Doppler is indicated following confirmation of echogenic bowel.

Fetal echogenic bowel is noted in up to 1 percent of second trimester sonograms and is usually associated with a normal fetus. In normal fetuses, it usually resolves over a period of weeks, with no adverse sequela.

Fetal echogenic bowel can be associated with underlying pathology, most commonly swallowed blood, aneuploidy, cystic fibrosis, growth restriction, infection, or a gastrointestinal malformation.

In the third trimester, echogenic bowel is common and a normal finding since meconium is present in the colon at this time and can be echogenic.

It is important to determine whether echogenic bowel is an isolated finding or other abnormalities are present that suggest an etiology. Women should be counseled about potential fetal disorders and offered appropriate testing.

Suggest the following approach when echogenic bowel is detected in the second trimester. • An experienced obstetric sonographer should perform a thorough ultrasound examination including a fetal anatomic survey with attention to the gastrointestinal tract, estimation of fetal size/growth, assessment of markers suggestive of aneuploidy, and evaluation for signs of fetal infection. • Offer parental cystic fibrosis screening and maternal serologic testing for cytomegalovirus and toxoplasmosis infection. • Offer amniocentesis for diagnostic testing: fetal karyotype and fetal testing for cystic fibrosis and for cytomegalovirus and toxoplasmosis infection if parental screening yields positive results.

Clinical examination • Serial measurement of symphysisfundal height (SFH) is recommended at each antenatal appointment from 24 weeks of pregnancy.

Women with a single SFH which plots below the 10thcentile or serial measurements which demonstrate slow or static growth by crossing centiles should be referred for ultrasound measurement of fetal size.

Women in whom measurement of SFH is Inaccurate • For example: • BMI>35 • Large fibroids • Hydramnios : Serial assessment of fetal size using ultrasound

Limited predictive accuracy • Marternal obesity • Abnormal fetal lie • Large fibroids • Hydramnios • Fetal head engagment

A. Customized SFH chart adjusted for maternal characteristics (Maternal height , weight, parity and ethnic group)

Observational studies suggest that customized SFH charts may improve the detection of a SGA fetus.

Risk factors for SGA fetus /neonate