A 10-year-old girl who is pregnant with twins after she was raped by a neighbour has been forced to continue with her pregnancy after human rights campaigners lost their fight to secure a legal route to abortion.

The plight of the girl, who is understood to be five months pregnant and lives in southern Senegal, highlights the heavy cost women and children are paying for a Napoleonic law on abortion that is still in force in the former French colony.

"She is going to have to go through with the pregnancy," said Fatou Kiné Camara, president of the Senegalese women lawyers' association. "The best we can do is keep up pressure on the authorities to ensure the girl gets regular scans and free medical care.

"Senegal's abortion law is one of the harshest and deadliest in Africa. A doctor or pharmacist found guilty of having a role in a termination faces being struck off. A woman found guilty of abortion can be jailed for up to 10 years."

Forty women were held in custody in Senegal on charges linked to the crimes of abortion or infanticide in the first six months of last year, official figures show. According to estimates, hundreds of women die every year from botched illegal terminations.

"For a termination to be legal in Senegal, three doctors have to certify that the woman will die unless she aborts immediately. Poor people in Senegal are lucky if they see one doctor in their lifetime, let alone three," Camara said.

"A single medical certificate costs 10,000 CFA francs ($20), which is prohibitive. We had a previous case of a raped nine-year-old who had to go through with her pregnancy. We paid for her caesarean but she died a few months after the baby was born, presumably because the physical trauma of childbirth was too great."

The women lawyers' association is lobbying MPs to align Senegal's abortion legislation with the African charter on women's rights, which the country ratified 10 years ago. Its provisions – legal medical abortion in cases of rape and incest, or where a woman's physical or mental health is threatened – have never been added to the statute book.

"The greatest unfairness is that the poor are the victims of our archaic legislation," said Camara, a law professor at Cheikh Anta Diop University in Dakar. "Anyone with enough money can easily have an abortion at a private clinic. But if you are poor you are expected to go through the legal motions or risk your life in a backstreet clinic."

Six years ago, the association opened a legal drop-in centre in Dakar to better deal with such issues. "We all work for free and we are open to everyone. But it is very clear that women's and children's rights are the ones that are most often ignored," Camara said.

The team is trained in trauma counselling and deals with a range of inquiries, from how to register a birth to where to hide from an abusive husband. The association can be contacted in person or via a freephone number.

"Most of the calls are from rural people and concern property rights and access to land," said Aminata Samb, 25, a law graduate who works with the association. "This morning a woman rang to say her husband had married another woman and was no longer taking care of her and her children. I inform the callers of their legal rights and tell them where to turn, should they want to exercise them. But many women just want to tell their story again and again. It makes them feel better."

Muslim Senegal is constitutionally secular, but customary law is in widespread use. At least 10% of girls are married before 14, and men can have up to four wives. But, according to Camara, religion and polygamy are not the cause of the rights shortfall. "Ignorance is the biggest enemy and it is a problem both among ordinary people and among people they look up to, like religious leaders," she said.

Since 2008, the women lawyers' association has trained more than 1,000 parajuristes, or legal lay people, to improve the handling of such issues. They are ordinary men and women who have been given a grounding in the law, enabling them to act as a first port of legal call in their communities.

Moussinatou Dramé, 29, a primary school teacher, works as a legal lay person in Pikine suburb near Dakar. "I often find myself mediating, between a husband and wife or between two sides of a family. I also try to explain to women the importance of registering their children's births and, if possible, of having a civil wedding, as well as a religious one, to increase their legal rights."

Amadou Aly Kane, a human rights lawyer, believes the country's parajuristes, while not unique in Africa, played a crucial role in improving access to justice for ordinary people. "They are more accessible than lawyers not just because they are free but because they are present at the grassroots of society where illiterate people would otherwise have no access to the law," he said. "There is no doubt that they are contributing to the improvement in human rights in Senegal."

Camara said the parajuristes, who uncovered the plight of the 10-year-old, were her eyes and ears on the ground. Terminations in such extreme cases should be made legal, she added. "Senegal must legalise medicalised abortion so that we never see any more cases like hers. Had we had time and had the girl's parents been willing, we could have asked a judge to consider guaranteeing immunity from prosecution to an [abortion] doctor," she said. "However, the family is poor; the process is difficult enough for them. They were just pleased when the rapist was arrested."

Alex Duval Smith travelled to Senegal with the EU, which supports the drop-in centres

• This article was amended on 13 May 2014 to protect the girl's identity and to clarify that she was understood to be five months pregnant at the time of writing.