Calculator Guide

• 2 or more high markers: high risk of early PE. Prescribe aspirin, serial PlGF and refer to Fetal Medicine.
• 1 high + 1 moderate: moderate-high risk. Prescribe aspirin and reassess with 2nd-trimester uterine artery PI and sFlt-1/PlGF.
• 1 high marker: aspirin according to the FMF combined risk; uterine artery PI check in the 2nd trimester.
• 2 or more moderate: close surveillance, consider aspirin, reassess in the 2nd trimester.
• 1 moderate: routine follow-up, integrating other clinical factors.
• All normal: baseline risk.

Aspirin ~150 mg every night from 11–14+6 wk until 36 wk, delivery or diagnosis of PE (FIGO 2019, regimen preferred by CaVeSal®). Alternative: 81 mg/day from 12–28 wk (ideally before 16) until delivery (ACOG PB 222, 2020).

Indications in the Calculator: high risk in first-trimester screening (uterine artery PI, PlGF, combination of markers) and pre-pregnancy obesity.

• 1st trimester: complementary element of preeclampsia screening. There is no single validated cut-off and it does not indicate aspirin on its own.
• 2nd/3rd trimester, with established PE/HDP — ≥0.78: suggests severe vascular involvement (PE with severe features). Integrate with BP, laboratory tests, sFlt-1/PlGF and fetal wellbeing.
• <0.78: does not rule out severity; clinical judgement decides.

• Enter the GA of the measurement: the Calculator reports the centile of the mean PI and compares it with the 95th centile for that GA.
• >95th centile for GA: fetal growth surveillance and follow-up Doppler at 28–32 wk.
• ≤95th centile: normal.

Fetal lung maturation and magnesium sulfate: see the cards Fetal lung maturation and Magnesium sulfate.

• MAP = (SBP + 2 × DBP) / 3.
• MAP >90 mmHg in the 1st trimester: higher risk of PE; consider aspirin according to the combined risk.
• MAP ≥105 mmHg: warning sign of gestational hypertension or PE, especially after 20 wk; assess proteinuria, sFlt-1/PlGF and liver and renal function.

• Robinson and Fleming formula (1975), the FMF standard, for CRL from 10 to 84 mm.
• With GA by CRL the Calculator corrects the LMP and recalculates the EDD (corrected LMP + 280 days).
• In the 1st trimester GA by CRL is the most accurate; if it differs from the LMP, ultrasound takes priority.

• Estimates GA with BPD, HC, AC and FL (Hadlock 1984) and compares the parameters with each other.
• Difference ≤7 days: concordant biometry, symmetric growth.
• 8–14 days: moderate discordance; monitor progression.
• Mean GA: average of the parameters entered.
• >14 days: significant discordance; the result shows which parameter is ahead or lagging.
• Head ahead with concordant AC and FL: not an FL/AC asymmetry; correlate with dating, EFW and Doppler.
• Lagging AC: consider asymmetric FGR (see the Growth tab). Lagging FL: assess humerus.
• FL, AC and HC are copied automatically to the FL/AC Asymmetry tab.

• GA is estimated from humerus and femur with the Chitty and Altman (2002) equations.
• Enter the GA by LMP or early scan to obtain the centile of each bone.
• Humerus or femur <3rd centile for GA: short long bone; confirm dating, measure the other long bones, look for signs of skeletal dysplasia and refer to Fetal Medicine.
• The humerus/femur ratio is reported as data, together with the expected value for GA; it does not define a diagnosis on its own.

• GA is estimated with the Snijders and Nicolaides (1994) equation. The rule TCD (mm) ≈ GA (weeks) holds only up to 20–21 wk.
• TCD is little affected by growth restriction: it helps confirm GA in FGR fetuses.
• Enter the GA by LMP or early scan to obtain the centile.
• TCD <5th centile for GA: suspected cerebellar hypoplasia; refer to Fetal Medicine and rule out Dandy-Walker and other CNS malformations.
• TCD >95th centile: review dating.

• Hadlock 1985: with Figueras, 4-parameter formula (BPD, HC, AC, FL) and, if any value is missing, the 3- or 2-parameter formula; with INTERGROWTH-21st, the 3-parameter formula (HC, AC, FL), the one that standard was built on.
• Figueras 2008 (Fetal Medicine Barcelona): select fetal sex; if unknown, the average of both sexes is used. Valid 24–42 wk.
• INTERGROWTH-21st 2020 (Stirnemann 2020): official equations for Hadlock EFW. Valid 18–40 wk (up to 41 if justified).
• The formula and chart used are shown below the result.

• EFW ≥4,500 g: severe macrosomia; planned caesarean recommended (ACOG/NICE). Shoulder dystocia risk 14–22 %.
• EFW ≥4,000 g: close surveillance; shoulder dystocia risk 3–4 %. In diabetic women consider caesarean. Ultrasound check at 38–39 wk.
• EFW 3,800–3,999 g: upper limit; serial biometry, especially in diabetic women.

• Exact HC centile by GA with the Chitty 1994 equation (derived HC): mean = −109.7 + 15.16·GA − 0.002388·GA³; SD = 3.913 + 0.2329·GA (mm, 12–42 wk).
• Z-score = (HC − mean) / SD for the exact GA. Example at 32+0 wk: mean 297 mm, SD 11.4 mm; −2 SD ≈ 274 mm and −3 SD ≈ 263 mm.
• Z <−3 SD: microcephaly, guarded prognosis; urgent referral to Fetal Medicine, neurosonography, rule out congenital infection (TORCH, Zika), chromosomal abnormality or genetic cause.
• Z between −2 and −3 SD: suspected microcephaly; targeted neurosonography, assess proportion with AC and FL, follow-up every 2–4 wk. Most of these fetuses have a normal outcome.
• Between −2 SD and P5: low HC (borderline); check in 3–4 wk.
• P3 (Z −1.88) is the neonatal criterion used by the CDC during Zika; it is almost equivalent to −2 SD (P2.3). Prenatal ultrasound uses −2 and −3 SD (ISUOG; WHO 2016).
• In asymmetric FGR or with uncertain LMP in the 3rd trimester, HC and FL are the most reliable parameters to estimate GA. In the 3rd trimester the LMP is not corrected: it is used as an approximate reference.

• Centile by exact GA with own equations fitted to the FMF model (Ciobanu 2019), range 20–42 wk.
• UA PI >P95: increased placental resistance.
• MCA PI <P5: cerebral vasodilation.
• CPR: its percentile by GA is reported with own equations fitted to the FMF model (Ciobanu 2019); the P5 varies with GA (e.g. ≈1.38 at 29–30 weeks and ≈1.44 at 33 weeks).
• CPR <P5: abnormal; cerebral redistribution, assess haemodynamic FGR. Confirm with a second measurement more than 12 h apart.

• Increased PI: venous dysfunction.
• Absent a-wave: severe decompensation.
• Reversed a-wave: severe decompensation; deliver.

• Normal PI: no advanced redistribution.
• Raised PI: possible advanced cerebral redistribution; correlate with CPR and biophysical profile.
• Reduced flow: onset of severe redistribution; intensive surveillance, repeat in 24–48 h.
• Absent diastolic flow: severe haemodynamic compromise; imminent delivery depending on context.
• Retrograde flow: maximal redistribution with left heart failure; urgent delivery.

• Mild pulsatility: intensive surveillance; repeat in 24 h; consider delivery according to GA.
• Overt pulsatility: late fetal decompensation with venous congestion; urgent delivery coordinated with neonatology.

Coordinate with neonatology and refer to a tertiary centre. Timing of delivery depends on GA, biophysical profile and progression. For lung maturation and neuroprotection, see the cards Fetal lung maturation and Fetal neuroprotection with magnesium sulfate.

Serial MCA PSV allows timing of the second intrauterine transfusion.

• Determine chorionicity and amnionicity in the 1st trimester.
• Monochorionic: serial Doppler due to the risk of twin-to-twin transfusion syndrome.
• Dichorionic: biometry every 4 weeks.
• Refer to Fetal Medicine.

• The Calculator compares fundal height with the 10th, 50th and 90th percentiles for GA. McDonald rule of thumb: FH (cm) ≈ GA ± 2 between 20 and 36 wk.
• <P10: rule out FGR, oligohydramnios or discrepancy with amenorrhoea. Ultrasound with EFW and Doppler (UA, MCA, CPR).
• >P90: rule out macrosomia, polyhydramnios, gestational diabetes, undiagnosed twins, fibroids or GA discrepancy.

Singleton pregnancy. In twins the targets are higher. The Calculator flags gain as excessive or insufficient when it deviates more than 1.5 kg from what is expected for the week.

• Obesity: aspirin to prevent PE (see the Preeclampsia tab), early screening for gestational diabetes, BP surveillance and referral to nutrition.
• Overweight: moderate risk of gestational diabetes, PE and macrosomia; GDM screening at 24–28 wk and BP surveillance.
• Underweight: risk of FGR and preterm birth; calorie-protein supplementation and serial biometry.
• Excessive gain: assess gestational diabetes and macrosomia. Insufficient: assess FGR, nausea or hyperemesis.

During antenatal care the Calculator assigns a probable group with the available data. The definitive group is assigned at admission for birth (WHO). For example, a nulliparous woman at term with a cephalic fetus is placed in group 1 assuming spontaneous onset; if induction is planned she moves to 2a and if caesarean is planned, to 2b. If birth occurs before 37+0 wk, she moves to group 10.

Only previous caesareans count: a myomectomy or other uterine surgery without caesarean does not change the group (WHO 2017).

The full classification and management by group are in the Emergencies guide: Robson classification and Management by group.

• Candidate: one previous caesarean with a low transverse scar.
• Favour success: previous vaginal birth and non-recurrent previous indication.
• Assess carefully: potentially recurrent previous indication; previous uterine surgery according to myometrial extent.
• Absolute contraindication: classical or inverted-T scar.
• Two or more caesareans: planned repeat caesarean per MSPBS Paraguay (vaginal birth is discouraged; uterine rupture ~1.4 %). If she arrives in the second stage: manage as one previous caesarean.
• International view: ACOG, RCOG and RANZCOG allow vaginal birth after 2 caesareans with senior obstetrician counselling; FIGO is more restrictive. With 3 or more, evidence is very limited.
• The Calculator estimates the probability of success with the Grobman score.
• Requirements: immediate surgical availability and informed consent; discuss the risk of uterine rupture (0.5–0.9 %). Misoprostol is contraindicated.

• Transverse or oblique lie (absolute indication).
• EFW ≥4,500 g (ACOG).
• Classical or inverted-T uterine scar.
• Breech presentation: caesarean recommended unless external cephalic version is successful (offer ECV from 36–37 wk if not contraindicated).
• Without a medical indication, planned caesarean is not performed before 39 wk.
• Short maternal stature with high EFW: suspected cephalopelvic disproportion.

• Preterm (<37 wk): assess lung maturation and coordinate with neonatology.
• Term (37–41+6 wk).
• Post-term (≥42 wk): increased risk; consider induction and biophysical monitoring.

Bishop score: see the Emergencies guide — Mode of delivery.

• The Calculator takes the trimester from the case GA; without GA it uses <11 g/dL.
• FIGO 2025 proposes <11 g/dL in all trimesters and postpartum, to unify the criterion and prevent postpartum haemorrhage. It is a valid reference; the Calculator uses the WHO 2024 thresholds.

• <150 ×10³/µL: thrombocytopenia; mild cases are usually gestational.
• <100: rule out HELLP and preeclampsia.
• <50: severe; urgent haematology.
• Neuraxial anaesthesia: possible with ≥70 ×10³/µL if there is no other coagulopathy or rapid fall.

• The Glucose field in the main form follows the protocol chosen in the module: with ALAD, 100–125 asks for a repeat; with ADA 2 steps, an isolated fasting glucose after 15 weeks is not diagnostic.
• Between 92 and 109 before 15 weeks, the Calculator shows both readings and leaves management to the physician. TOBOGM (Simmons 2023): benefit of early treatment in the higher band; possible excess SGA when treating the lower band.
• MSPBS (Paraguay): 2 h 140–152 = high risk of developing diabetes (moderate card).
• Two-step: the Calculator uses 50 g ≥130; ADA/ACOG accept 130, 135 or 140. ACOG accepts 1 abnormal value and the NDDG thresholds.
• ADIPS 2025 (Australia): 95 / 191 / 162 mg/dL; reference only.
• Metformin does not prevent GDM (ADA 2026, meta-analysis of 11 RCTs). Postpartum OGTT at 4–12 weeks.

• Use the laboratory pregnancy range. If not reported: TSH upper limit 4.0 µIU/mL (ATA 2017; the trimester no longer changes the cutoff).
• Check anti-TPO if TSH is >2.5 in the 1st trimester (ATA 2017, rec. 28) or >3.0 in the 2nd–3rd (CaVeSal® suggestion).

• Grey zone (CaVeSal® suggestion): TSH >2.5 in T1 or >3.0 in T2–T3 and ≤4.0: check anti-TPO; if positive, consider levothyroxine.
• History of the cutoffs: ATA 2011 and Endocrine Society 2012: 2.5 / 3.0 / 3.0 by trimester. ETA 2014: 2.5 / 3.0 / 3.5. ATA 2017 replaced them with the laboratory range or 4.0.
• Trials: CATS (Lazarus 2012, 21,846 women, treatment at ~13 weeks: IQ at 3 years 99.2 vs 100.0) and Casey (2017, TSH ≥4.0, treatment at ~17 weeks: IQ at 5 years 97 vs 94) showed no neurodevelopmental benefit. The link between high TSH and cognitive deficit is observational.
• Preconception: treated hypothyroid women, TSH between the lower limit and 2.5. IVF/ICSI with subclinical hypothyroidism: levothyroxine with a TSH goal <2.5 (ATA 2017, rec. 20).
• Low TSH in T1: may be physiological due to hCG; confirm with free T4 and, if Graves disease is suspected, TRAb.
• Low free T4 with normal TSH: isolated hypothyroxinemia; not routinely treated. Free T4 varies by method and trimester.

• The Endocrine Society 2011 range <20 / 20–29 / ≥30 is the one laboratories report. IOM 2011 sets sufficiency at ≥20 (bone health). Bouillon 2017 compares the societies.
• 20–29 ng/mL: grey zone; supplement at the physician's discretion.
• WHO 2020: no routine supplementation in pregnancy; supplement if deficiency is documented or suspected.
• Endocrine Society 2024: empirical supplementation in pregnancy without testing (trials used 600–5000 IU/day, mean ~2500); it no longer endorses sufficiency cutoffs.
• Neither recommends routine testing, including for obesity or dark skin. The choice is at the physician's discretion.

• National criterion (Paraguay): Manual Nacional de Normas de Atención de las Principales Patologías Obstétricas (MSPBS/SPGO 2018), ch. 5. Diagnosis: itching + bile acids ≥10 µmol/L and/or raised enzymes or bilirubin.
• UDCA 10–16 mg/kg/day in 2 doses (start 900 mg/day, maximum 1200 mg/day). Follow-up: liver profile, bile acids and PT every 1–2 wk; CTG every 3–7 days.
• Regional reference (MINSAL Chile 2015): anicteric 38 wk; icteric (bilirubin >1.2 + raised enzymes) 36 wk.
• International reference (RCOG GTG 43, 2022): diagnosis ≥19 µmol/L; 19–39 birth by 40 wk; 40–99 38–39 wk; ≥100 35–36 wk. With ≥100, consider earlier delivery.
• In all cases: deliver if fetal wellbeing is compromised, regardless of GA.

• Folic acid: 0.4–0.8 mg/day from preconception to at least 12 wk. High dose with a previous NTD (previous pregnancy, or the woman or her partner with an NTD), epilepsy or antiseizure drugs, obesity or diabetes: 4 mg/day (ACOG PB 187, CDC) or 5 mg/day (NICE, RCOG), from 3 months before conception to 12 wk; then return to the standard dose. Another previous malformation does not justify it. In Obstetric history, the “Previous NTD” box activates the high dose.
• MTHFR: folic acid remains the standard (CDC), as it is the only form proven to prevent NTDs. Methylfolate (5-MTHF) 400–800 µg/day is an optional alternative.
• Iron: prophylaxis 30–60 mg/day elemental iron (WHO). Anaemia: 120 mg/day until Hb normalises, then back to prophylaxis. Hb <7 g/dL: IV iron from the 2nd trimester and consider transfusion according to the clinical picture.
• Calcium: requirement 1000 mg/day (1300 under 19 years), the same as outside pregnancy. WHO: 1.5–2 g/day in 3 doses in low-intake populations. Cochrane 2025 (10 trials, 37,504 women): no difference in pre-eclampsia in the large trials. Physician's decision; separate from iron.
• Iodine: 150 µg/day supplement (potassium iodide) from preconception; total intake target 250 µg/day. Avoid supplements >500 µg/day and seaweed.
• Omega-3: with risk of preterm birth, 500–1000 mg/day DHA+EPA before 20 wk (Cochrane 2018: 42% fewer births <34 wk). Effect on pre-eclampsia uncertain.
• Vitamin D: see the vitamin D section in this tab.

• Calculate button: every entered item returns a result and a management step, also when normal. If a test is already entered its result is used; if it is missing and needed, it is suggested.
• Labs within range: summary of the normal values. Repeat according to the Lab schedule. Fasting glucose <92 mg/dL before 24 wk: 75 g OGTT at 24–28 wk.
• Non-reactive serologies (HIV, syphilis, HBsAg, hepatitis C, Chagas): repeat according to the Lab schedule.
• Anti-HBs negative: not immune to hepatitis B; the vaccine is safe in pregnancy, give it if HBsAg is negative.
• CMV IgG negative: susceptible; hygiene measures (hand washing after changing diapers, do not share utensils with young children).
• Group B streptococcus negative: no intrapartum prophylaxis; the result is valid for 5 weeks.
• Recurrent pregnancy loss (2 or more miscarriages): antiphospholipid work-up (lupus anticoagulant, anticardiolipin, anti-β2 glycoprotein I), TSH and anti-TPO, early follow-up.
• Grand multiparity (5 or more births/caesareans): higher risk of postpartum haemorrhage and malpresentation; birth plan with active management of the third stage.
• 2 or more caesareans: planned repeat caesarean per MSPBS Paraguay; if she arrives in the second stage, manage as one previous caesarean.
• Normal 1st-trimester screening: scan without markers, low combined risk or low-risk cell-free DNA: anomaly scan at 20–22 wk. Age ≥35 with scan only: offer cell-free DNA or combined test. If screening is already entered, the age card does not request it again.
• Anomaly scan without anomalies: 3rd-trimester growth according to overall risk; suggests cervical length and 2T uterine PI if not recorded.
• Fetal weight: P10–P89, appropriate growth. P3–P10 without Doppler: request Doppler (UA, MCA/CPR, uterine) to distinguish SGA from FGR.
• Supplementation: prophylactic iron 30–60 mg/day with normal Hb (WHO); with MTHFR, standard folic acid (methylfolate optional); vitamin D according to the entered value; calcium at the physician's discretion (WHO in low intake vs. Cochrane 2025 no effect on pre-eclampsia); see Supplementation in pregnancy.