Experts have debunked the myth abortion causes infertility and breast cancer.

Abortion is a polarising issue.

The Government's potential move to take the procedure out of the Crimes Act and treat it as a health issue has sparked debate.

Emotional arguments are coming out from both sides and it can be hard to distinguish fact from fiction.

So what is the science behind the claims? We asked medical experts and researchers about commonly held beliefs on abortions.

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Who is getting abortions and why?

When people think of abortion, they often envision irresponsible teenagers relying on the procedure as contraception. But statistics and research don't support that stereotype.

About one in four Kiwi women are estimated to have terminated a pregnancy, which means we probably all know someone who has had an abortion – they might just not have told us.

The majority of women getting an abortion already have children (57 per cent last year).

STOCK Forty per cent of all pregnancies are unplanned, and about one in five pregnancies ends in abortion.

Women in their late 20s are having the largest number of abortions, while rates continue to decline among teens.

Last year, 13,285 induced abortions were performed. Of these, 1414 involved teenagers, according to Stats NZ.

It's also worth noting that 40 per cent of all pregnancies are unplanned. Contraception can and does fail.

Condoms have a "typical use" failure rate of 15 per cent, while the two most popular contraceptives – the pill and Depo Provera (a three-monthly hormonal injection) – have "typical use" failure rates of 8 per cent and 3 per cent respectively.

But why are some women choosing to terminate a pregnancy? Well, there is the official reason, and then there are the real reasons.

About 98 per cent of abortions in New Zealand are performed on the grounds that the pregnancy endangers the mental health of the mother.

That's because abortion is technically a crime in New Zealand. Two certified medical practitioners must deem the abortion medically necessary or justified for it to be legal.

Legal grounds to terminate a pregnancy under 20 weeks' gestation include serious danger to life, physical health, or mental health. Incest, and foetal abnormality also provide legal grounds for termination, but rape does not. Contraceptive failure and inability to support a child are not legal grounds for abortion.

Jane Zusters A photograph of a 1978 pro-abortion protest in Christchurch from artist Jane Zusters' book, Where Did You Go To My Lovelies?

So most women say their mental health will suffer if they want to access an abortion. But in reality, things are much more complex than that.

Data collected as part of the Dunedin longitudinal study found that the most common reason given for having an abortion was not being ready, followed by relationship reasons, including being in the wrong relationship and being alone.

Researchers working on the Christchurch longitudinal study also asked women why they were having abortions, but did not analyse and publish the results.

Otago University associate professor Joe Boden, who has worked on the study for more than 10 years, says the main reasons women cited were: they weren't ready, they felt they couldn't afford to have a child, and they were not with the right partner.

Christchurch GP Pippa McKay has been performing abortions for over 25 years at the public hospital. She says she sees women from age 12 to 49 from all sorts of backgrounds in her clinic.

She even sees religious people and people who say: "I don't believe in abortion, but ...".

"We have people who protest outside and they've had children coming to us."

ALEXANDER TURNBULL LIBRARY A placard at the 1978 International Women's Day march in Wellington.

What are the risks of having an abortion?

There are two types of abortions: medication (taking pills), which women may choose up to nine weeks into a pregnancy; and surgical (using suction and sometimes forceps).

Pippa McKay says the most common side-effect of an abortion she sees is relief.

Complications are rare and the risks of having an abortion are much lower compared to the risks of continuing a pregnancy to term.

A small number of people may experience bleeding, and a smaller number may retain product after the procedure, leading to heavy bleeding and an antibiotics prescription.

ANDREW GORRIE/STUFF Pro-choice protesters at Parliament in May.

What about infertility and breast cancer?

McKay says anti-abortionists have been trying for years to push the myth that abortions cause infertility and breast cancer, but these claims have been debunked by research. "It's scaremongering."

According to the UK's Royal College of Obstetricians and Gynaecologists, if you have an abortion in a safe and legal setting, there is "no proven association" with infertility.

A research analysis looking at 53 studies, which included 83,000 women with breast cancer, found that having an abortion does not increase a woman's risk of developing breast cancer.

What about depression and other mental health issues?

This is a hotly debated question, and a complicated one.

Anti-abortion groups in New Zealand often cite 2008 research done by Otago University, which suggested there was a 20 per cent increased risk of mental health problems among women who have had an abortion.

But Boden says it's important to note that the study found this effect was confined to people who were conflicted about having an abortion – they felt guilty, or uncertain whether it was the right thing to do.

HAMISH McNEILLY/STUFF Men protest over the abortion clinic at Dunedin Hospital in October.

The increase in risk is also no greater than the risk posed by many other life events.

For Boden, this result does not mean abortion should be restricted, or that women should be forced to attend counselling before having one. It just means the option should be there for those who want to access it.

Clinicians could simply ask women how they feel about the procedure and, if they say they are having mixed feelings about it, they should be offered services to help with that.

But how do women who get an abortion fare, mentally, compared with those who are forced to bring an unwanted pregnancy to term?

A study published in the JAMA in 2017 compared mental health outcomes over five years of women who wanted an abortion but didn't get one, and women who did have a termination.

The study, which included 956 women, found that a week after seeking an abortion, women who were denied it reported significantly more anxiety symptoms and lower self-esteem and life satisfaction, but similar levels of depression, as women receiving abortions. Outcomes improved or remained steady over time.​

Can a foetus feel pain?

First it's worth noting that the gestational age starts running from the first day of the woman's last period – before she actually got pregnant.

In New Zealand last year, 94 per cent of abortions were performed within 14 weeks from a woman's last period.

Almost two-thirds happened within nine weeks from her last period.

At nine weeks, the embryo is about the size of a peanut and has a microscopic heart. McKay says the embryo becomes a foetus around 12 weeks.

Foetal physiology expert professor Laura Bennet, from the University of Auckland, says embryos most definitely cannot feel pain and there is no evidence that foetuses can feel it either.

Skin receptors start appearing around seven weeks, but to feel pain, you also need nerve fibres to send a pain signal to the spinal cord and up into the brain. And your brain needs to be developed to the stage where it can process the pain signal.

"A foetus does not have the anatomy to process sensations in the way we understand pain. And I would argue that at no time will they feel pain because they are not awake to feel pain."

A report on foetal pain and awareness published by the UK Royal College of Obstetricians and Gynaecologists concludes that research so far has found that "pain is not possible until after 24 weeks".

By 24 weeks, or six months, abortions are rarely performed.

The pathways to the brain develop between 25 and 30 weeks, but even then Bennet says the foetus would need to be awake to feel pain.

She says extensive research has found no physiological evidence that the foetus is ever awake in utero. "Babies are awake and conscious when they are born."

Our currents laws work just fine, don't they?

The Law Commission, in its advice to the Government this year about abortion law reform, said our current rules lead to delays and present barriers for women seeking abortion services.

Women may have to travel to have multiple appointments and, depending where they live, their abortion could be delayed because of it.

In the past decade, about 1500 women in New Zealand have been refused an abortion by the state.