Kiwi mothers of children with disabilities caused by exposure to an anti-convulsant medication during pregnancy want answers on why they were not warned earlier of its dangers to unborn babies.

They are calling for the Government to launch an inquiry into the use of anti-epileptic drugs in pregnant women.

The UK has this week moved to further restrict sodium valproate - also known as Epilim - requiring doctors to ensure women and girls are fully aware of the risks and have patients sign an acknowledgement form confirming this at least every year.

Sodium valproate is commonly used to treat epilepsy and other neurological conditions.

Studies first confirmed that it could cause birth defects including spina bifida and developmental delays during the early 1980s.

However, it wasn't until more than two decades later - in 2005 - that New Zealand's prescription drug regulator Medsafe officially recommended sodium valproate not be used during pregnancy.

Sharon Hodgson, the UK Labour party's Shadow Health Minister, said this week that a public investigation was needed there to find out why it was prescribed to pregnant women for so long.

Denise Astill, founder of Foetal Anticonvulsant Syndrome New Zealand (FACSNZ) which advocates for families of children affected by foetal valproate syndrome, has started a petition for the New Zealand Government to do the same.

"The healthcare professionals and the government bodies have not done enough. To this day there are babies still being harmed because healthcare professionals aren't providing informed consent," she said.

The Centre for Adverse Reaction Monitoring (CARM) has received 27 reports of foetal abnormalities linked to Epilim since 1978. Of these five babies died and 13 had behavioural or neurodevelopmental problems.

However, Astill told the Weekend Herald she believed those figures were under reported as many parents were not aware Epilim had affected their children's development.

Some international studies have estimated that up to 40 per cent of children born to females who have taken sodium valproate while pregnant have developmental delays and 10 per cent have physical abnormalities. Other reports say the developmental delays are between 14 and 20 per cent.

Astill said she wanted the Ministry of Health to monitor more closely the use and side effects of sodium valproate during pregnancy.

Patients or their doctors are responsible for reporting adverse reactions, including birth defects to CARM.

Astill said medical professionals needed to do more to ensure patients were aware fully aware of the risks.

"When they're first prescribed those medications they need to be informed. It's an ongoing conversation. They need to be getting reviewed yearly, especially when they're in child bearing age.

"It's definitely about upskilling and educating the health care professionals but also allowing the women and empowering the women with that information as well."

She had voiced her concerns to the ACC Minister Iain Lees-Galloway and hoped to meet with Minister of Health David Clark too.

A spokeswoman for Clark's office said Clark and Lees-Galloway met to discuss the issue last year and were seeking advice from officials.

Waitara mum-of-three Trish Pringle, whose 2-year-old daughter Danae has multiple health issues due to exposure to Epilim in the womb, echoed Astill's concerns.

She told the Weekend Herald she was prescribed Epilim after being diagnosed with epilepsy in 1998 but was not aware that it could affect babies in utero until 2015.

"I was absolutely blindsided," she said recalling the day she heard a paediatrician speak about the risks at an epilepsy seminar about three months after Danae, the youngest of three girls, was born.

Danae has since been diagnosed with cognitive and speech delays and physical disabilities caused by the drug.

Pringle said she had spoken to doctors about taking sodium valproate during pregnancy when she and her husband started planning their family in 2008 and was never told about the risk of developmental delays.

"I was reassured that as long as I took folic acid it would counteract spina bifida and neural tube defects. All those warnings were out and the medical professionals knew about this and did not warn me. It could have been prevented if we were informed.

"The New Zealand Government needs to front up once and for all. These families need answers and justice."

Medsafe acting group manager Alison Cossar said the Ministry of Health had discussed whether to enforce additional restrictions with the manufacturer of Epilim, Sanofi.

"These communications continue."

Warnings about the risk Epilim posed to unborn babies were printed on the medication's packet, Cossar said.

The Ministry expected doctors to inform patients about the risks and benefits of medicines and were obliged to notify pregnant women taking sodium valproate about the risks.

A spokeswoman for Sanofi said the company had repeatedly notified international medicine regulators of the risks of developmental disorders to foetuses.

Neurologist Dr Elizabeth Walker said although other anti-convulsants were available in New Zealand sodium valproate was sometimes the only drug that effectively controlled epilepsy patients' seizures.

Uncontrolled epilepsy could harm unborn children and females prescribed anti-convulsant medication should not stop taking it without advice from their doctor.

Making patients sign a form acknowledging they understood the risks each year before prescribing sodium valproate would not work in practice, she said.

Instead, the best way of preventing birth defects was ensuring GPs, who often renewed patients' prescriptions, understood the risks and communicated them to patients.