Omeprazole in pregnancy: what the evidence says

Heartburn and gastro-oesophageal reflux are extremely common in pregnancy, affecting up to 80% of women by the third trimester.

In my practice, I am frequently asked whether omeprazole can be safely taken during pregnancy.

The BNF states that omeprazole is 'not known to be harmful' in pregnancy.

This is an important classification: it means that available evidence does not suggest harm, although absolute safety cannot be guaranteed for any medication in pregnancy.

Key evidence:

• A large Danish cohort study of over 5,000 pregnancies exposed to PPIs (primarily omeprazole) found no increased risk of major birth defects, spontaneous abortion or preterm birth
• The UK Teratology Information Service (UKTIS) states that omeprazole can be used in pregnancy when clinically indicated
• A meta-analysis published in the American Journal of Gastroenterology concluded that first-trimester PPI exposure was not associated with an increased risk of major malformations

Despite this reassuring data, the principle of using the minimum effective treatment always applies in pregnancy.

I advise a stepwise approach, starting with non-drug measures before considering medication.

While omeprazole has not been associated with teratogenicity at any stage of pregnancy, I find it helpful to discuss the evidence by trimester.

First trimester:

This is the period of organogenesis, when concerns about teratogenicity are highest.

The available data from large cohort studies and meta-analyses do not show an increased risk of major malformations with omeprazole use in the first trimester.

However, I always try to manage reflux with lifestyle measures and antacids during early pregnancy if possible.

Second trimester:

Reflux symptoms often worsen during the second trimester as the uterus expands. If antacids are insufficient, omeprazole 20 mg once daily can be prescribed.

The evidence for safety during this period is robust.

Third trimester:

Symptoms peak in the third trimester. There is no evidence that omeprazole use near term affects labour, delivery or neonatal outcomes.

The drug does cross the placenta, but no adverse fetal effects have been demonstrated.

Breastfeeding:

Omeprazole is present in breast milk in small amounts. The BNF states it is 'not known to be harmful' during breastfeeding.

The NHS advises that it is usually safe to take while breastfeeding, as the amount passing to the infant is minimal.

Before prescribing omeprazole in pregnancy, I always discuss non-pharmacological approaches. NICE recommends these as first-line management for pregnancy-related reflux.

Dietary modifications:

• Eat smaller, more frequent meals rather than three large ones
• Avoid eating within three hours of bedtime
• Identify and avoid personal trigger foods (common culprits include spicy dishes, citrus fruits, chocolate, caffeine and carbonated drinks)
• Eat slowly and chew food thoroughly

Positional measures:

• Elevate the head of the bed by 10 to 15 cm using blocks or a wedge pillow
• Sleep on the left side, which keeps the gastro-oesophageal junction above the level of gastric acid
• Avoid bending forward or lying flat after meals

Other lifestyle adjustments:

• Wear loose-fitting clothing to avoid pressure on the abdomen
• Maintain appropriate weight gain as advised by your midwife
• Avoid smoking (which also relaxes the lower oesophageal sphincter)

If these measures do not provide adequate relief, the stepwise pharmacological approach is: antacids first (such as Gaviscon Advance), then ranitidine (if available), and finally omeprazole if symptoms remain uncontrolled.

If a patient is reluctant to take omeprazole during pregnancy, or if I feel a less potent option may suffice, there are several alternatives to consider.

Antacids (e.g. Gaviscon Advance):

Alginate-containing antacids are considered first-line pharmacological treatment for reflux in pregnancy. They form a raft on top of the stomach contents, reducing reflux.

They are available without prescription and have an excellent safety profile. Avoid antacids containing sodium bicarbonate in large amounts.

H2 receptor antagonists:

Ranitidine was previously the preferred H2 blocker in pregnancy, but it was withdrawn from the UK market in 2020 due to NDMA contamination concerns.

Famotidine is available and has a reasonable safety profile, though less pregnancy data exists compared with omeprazole.

Other PPIs:

Among PPIs, omeprazole has the largest body of safety data in pregnancy. Lansoprazole is classified similarly in the BNF ('not known to be harmful').

Esomeprazole, the S-isomer of omeprazole, is expected to have a comparable safety profile.

I always remind patients that untreated severe reflux carries its own risks, including poor nutrition, sleep deprivation, oesophageal inflammation and reduced quality of life.

These factors must be weighed against the theoretical concerns about medication use.

While reflux in pregnancy is common and usually benign, there are situations where medical review is important.

See your GP or midwife if:

• Lifestyle changes and antacids are not controlling your symptoms
• You are vomiting frequently or losing weight
• You have difficulty swallowing or pain on swallowing
• You are passing dark or black stools
• Symptoms started for the first time after 20 weeks (to exclude pre-eclampsia-related epigastric pain)

Important safety note:

Severe upper abdominal pain in the second half of pregnancy should not be assumed to be simple reflux. Epigastric pain is a recognised symptom of pre-eclampsia and HELLP syndrome.

If you develop sudden, severe upper abdominal pain with headache, visual disturbance, or swelling, seek immediate medical assessment.

Your omeprazole dose should be reviewed after delivery, as many women find their reflux resolves completely once the baby is born.

Continuing a PPI without reassessment is unnecessary for the majority of patients.