FGAs provide the most robust long-term teratogenicity database of any antipsychotic class in pregnancy.

Haloperidol — the "Gold-Standard" FGA in Pregnancy

• Haloperidol has the largest individual FGA exposure database. Consistent with FDA labeling and published epidemiologic studies, available data have not established a drug-associated risk of major birth defects or miscarriage; clinicians should verify the exact wording against the current decanoate label, as pregnancy-labeling language has been revised over time.10
• The oral haloperidol label reports no teratogenic effect in rats, rabbits, or dogs. Cleft palate was seen in mice at roughly 15× the maximum recommended human dose, but is regarded as a nonspecific response to stress or nutritional imbalance rather than a drug-specific effect.1112
• Isolated case reports describe limb malformations after maternal haloperidol use, but these involved concomitant drugs of suspected teratogenic potential, and causality was not established.1013
• The Schoretsanitis et al. (2020) systematic review found a mean umbilical-cord-blood penetration ratio of 0.66 (SD 0.40) — moderate placental transfer, similar to olanzapine (0.71) and higher than quetiapine (0.24).14

Chlorpromazine

The FDA label states that safety in pregnancy has not been established, and notes reported instances of prolonged jaundice, extrapyramidal signs, and hyper- or hyporeflexia in newborns of mothers who received phenothiazines.1516 Rodent reproductive studies showed potential embryotoxicity, increased neonatal mortality, and nursing transfer, with decreased offspring performance; the label notes the possibility of permanent neurological damage cannot be excluded.15 This uniquely cautionary language reflects an older labeling era rather than definitive evidence of harm, but combined with chlorpromazine's unfavorable metabolic and autonomic profile, it supports a second-line position.

Fluphenazine

The label states safety in pregnancy has not been established; the class-wide neonatal EPS warning applies.17 Availability as a long-acting injectable (decanoate) can be advantageous for adherence in schizophrenia.

Thioridazine

The label reports that animal reproductive studies and clinical experience have not shown a teratogenic effect.18 However, thioridazine carries a boxed warning for QTc prolongation, Torsades de pointes, and sudden death — a 50 mg dose produced a mean maximum QTc increase of ~23 msec, with greater prolongation expected at clinical doses — and is contraindicated with other QTc-prolonging drugs, CYP2D6 inhibitors, and in congenital long-QT syndrome.1819

The choice between high- and low-potency FGAs is a deliberate trade-off between neurological and metabolic risk.

High-Potency FGAs (Haloperidol, Fluphenazine)

• Neurological risk — HIGH. Potent D₂ blockade → higher risk of maternal EPS (dystonia, akathisia) and neonatal EPS (hypertonia, tremor, feeding difficulty).1113
• Metabolic risk — LOW. The Swedish register confirmed FGAs were not associated with GDM or LGA infants; two 2025 meta-analyses agreed (FGA GDM RR 1.31; 95% CI 0.29–2.32 in Liu & Zhao; no increased risk in Zhang et al.).345 One caveat: an earlier Swedish study (Bodén et al. 2012) found a GDM signal for a broad "other antipsychotics" category (aOR 1.77) that included some FGAs, so the FGA "no increased risk" conclusion rests mainly on the more recent, drug-class-specific Heinonen 2022 analysis.26

Low-Potency FGAs (Chlorpromazine, Thioridazine)

• Neurological risk — LOWER. Less D₂ blockade → lower EPS risk, but stronger anticholinergic, antihistaminic, and alpha-adrenergic effects.
• Metabolic risk — HIGHER. Potent H₁ blockade → weight gain, sedation, glucose intolerance. Alpha-1 blockade → orthostatic hypotension (falls; reduced uterine perfusion).1518
• Cardiac risk (thioridazine). QTc prolongation with boxed warning.19

The consensus: neonatal EPS is transient (resolving within 2–14 days) and manageable with supportive care in a standard nursery, whereas GDM and macrosomia carry lasting implications — increased cesarean delivery, shoulder dystocia, neonatal hypoglycemia, and long-term metabolic programming for mother and child. High-potency FGAs are therefore preferred when an FGA is indicated.3

A. Neonatal EPS & Withdrawal

• Severity. Variable: most cases are self-limited, but some neonates have required intensive-care support and prolonged hospitalization.1120
• Duration. Typically resolves within 2–14 days postpartum, manageable with supportive care (swaddling, quiet environment, assisted feeding).67
• Risk factors. Higher maternal dose, high-potency agents (haloperidol > chlorpromazine), and third-trimester use near delivery.11

B. Fetal Growth — the FGA Paradox

Unlike SGAs (which tend toward macrosomia via maternal hyperglycemia), FGAs show the opposite growth pattern:

• Joseph-Delaffon et al. (2024) meta-analysis: FGAs were associated with small-for-gestational-age <3rd percentile (OR 1.37; 95% CI 1.02–1.83) and lower mean birth weight (MD −135 g; 95% CI −203 to −66). SGAs, by contrast, were associated with large-for-gestational-age >97th percentile (OR 1.56; 95% CI 1.31–1.87).7
• Lin et al. (2022) Taiwan cohort: among antipsychotic-treated women, odds of low birth weight were higher with SGAs than FGAs (aOR 1.32; 95% CI 1.04–1.68), favoring FGAs on birth-weight outcomes.22
• Interpretation: the modest birth-weight reduction with FGAs likely reflects the absence of metabolic effect (no maternal hyperglycemia → no fetal hyperinsulinism → no overgrowth), generally a favorable trade-off versus the macrosomia risk of high-metabolic SGAs.

C. The "Hypotension Hazard" (Low-Potency Only)

Chlorpromazine and thioridazine cause significant alpha-1 blockade. Maternal: orthostatic hypotension, especially in the third trimester when pregnancy vasodilation compounds the effect; the chlorpromazine label notes hypotension rarely resulting in cardiac arrest.15 Fetal: brief reductions in uterine blood flow if maternal pressure drops sharply. Prevention: slow position changes, adequate hydration, third-trimester compression stockings, and avoiding concomitant antihypertensives where possible.

Although not FDA-approved for this indication, haloperidol and other D₂ antagonists are used as antiemetics in refractory hyperemesis gravidarum (HG).

• RCOG & ACOG. Phenothiazines (promethazine, prochlorperazine) are recommended as first-line pharmacotherapy alongside doxylamine–pyridoxine; dopamine antagonists (metoclopramide, domperidone) are second-line.24
• AGA Clinical Practice Update (2024). A Cochrane review found no significant efficacy difference among metoclopramide, ondansetron, and promethazine for HG. Phenothiazines and metoclopramide carry a risk of extrapyramidal effects; the drug should be withdrawn if these occur.25
• Safety. Cochrane and systematic reviews of antiemetics (including phenothiazines and dopamine antagonists) reported no safety signal, no increased teratogenesis, and no other adverse pregnancy outcomes.24
• Practical note. When haloperidol is used for HG it is typically low-dose (0.5–2 mg) and short-duration. Its metabolic neutrality is an advantage over ondansetron (QTc concerns) in patients already on other QTc-prolonging medications.

Haloperidol

Primarily metabolized by CYP3A4 (with CYP2D6 and CYP1A2 contributions). CYP3A4 activity rises substantially in pregnancy — a general estimate of ~50–100% for CYP3A4 substrates broadly, not a haloperidol-specific figure. Drug-specific data are more limited, but a 2026 systematic review reported haloperidol plasma concentrations falling by up to ~52% in the third trimester, consistent with declining levels across gestation.11

• Action. If breakthrough psychotic symptoms emerge in T2/T3, consider a trough level and an upward dose adjustment. Postpartum, CYP3A4 returns to baseline — the dose may need reduction to avoid toxicity.
• Decanoate (LAI). Dosed every 4 weeks; provides stable levels unaffected by pregnancy-related GI changes, but the long duration means adverse effects cannot be rapidly reversed.10
• Smoking. CYP1A2 plays only a minor role in haloperidol metabolism, so the cessation effect is less dramatic than with clozapine or olanzapine — but levels should still be monitored.

Placental Transfer (Schoretsanitis 2020)

Chlorpromazine is extensively metabolized by multiple CYP enzymes; its label notes placental transfer and nursing transfer in animal studies.15

Patient Script — Why We Prefer High-Potency Agents

EMR Documentation Template

Quick Neonatal Phenotype by Potency