‘Dilva, 25, is seven months pregnant. Her blood group is Rh(D)- but her foetus’ is Rh(D)+. Her antibodies are attacking her foetus’ red blood cells. The baby has severe anaemia,” Edwige Prel is briefing her colleague Yohanna Depierre, who is driving an ambulance down the motorway to Grande-Synthe, a commune in the third-largest suburb of Dunkirk, in the Nord-Pas-de-Calais region of France.

Prel and Depierre are both midwives who have given up 14 days of annual leave to volunteer for Gynaecology Without Borders (known as Gynécologie Sans Frontières, GSF). Founded in 1995, the French non-profit organisation provides emergency medical aid to women affected by conflict, epidemics and natural disasters. GSF’s midwives and gynaecologists have worked on missions across the world, from Afghanistan and Bangladesh to the Democratic Republic of the Congo, and, since 2015, in the Pas-de-Calais, France.

Following the demolition of the “Jungle” in October 2016 and the fire that engulfed the “Camp de la Linière” at Grande-Synthe in April 2017, GSF stayed put. Today, five volunteers (on rotation) continue to provide female refugees and asylum-seekers with emergency medical assistance.

Prel is worried about Dilva. “Her last baby passed away a few days after birth. We need to check if the baby is still alive.” She steps out of the ambulance and works her way through a crowd of men, past riot police and into a gymnasium that was transformed into an emergency shelter last December. “Today we are doing an ultrasound.”

Yohanna Depierre waits outside a consultation room in a hospital in Grande-Synthe. Inside Dilva, seven months pregnant, is having an ultrasound scan. Photograph: Alice Rowsome/The Guardian

Dilva’s blood type isn’t the only reason her pregnancy is high-risk. Originally from Kurdistan, Iraq, she fled last summer before fighting intensified during the Iraqi Kurdistan independence referendum. She has been stuck here since October and spends most nights attempting to stow away on lorries – no small feat with a swollen belly and fear for her child’s life.

While some refugees feel “blessed” to end their journeys in France, some want to claim asylum in the UK. “My mother and father live in Birmingham. I want to be close to them for the birth,” Dilva whispers to me in the hospital waiting room.

A few miles away, in an undisclosed location, is GSF’s safe house. It is run by 30-year-old Violaine (who doesn’t want to share her full name). With only two bedrooms and six spaces, deciding who is most vulnerable is not always simple, she explains, topping up a drawer with sanitary towels.

At the moment there is 31-year-old Maryam, an activist and political refugee. She is the only Iranian woman known ​by​ the volunteers​ ​to be​ ​in Calais at present, so she should not be alone in the forest, where most women survive by looking out for each other in small friendship groups, often determined by language. Maryam tried it once. “I picked her up in the morning. She was sobbing and completely traumatised,” says Violaine.

Then there is 24-year-old Joy. A lesbian from Nigeria, where homosexuality is still punishable by death in certain regions, she was told about “The Lady”, a woman whom she heard could help her seek asylum in Italy. But she was tricked and ended up as a sex slave, owing her traffickers around €50,000 (£44,300). After three years, with her debt still unpaid, she escaped and landed in a detention centre in Lille, France. Once she had been released, GSF took her to their safe house and helped her gain access to medical and psychological care. They are currently challenging the local council, which wants Joy repatriated to Italy. Joy wants to go anywhere but.

Except for Maryam and Joy, most people who stay in the safe house are minors. Kidisti and Milka, both 17, fled Eritrea at 15. “The regime in Eritrea is not good,” Kidisti explains, in perfect English sitting on a pull-out sofa-bed in the living room. “Military conscription for boys and girls is mandatory and indefinite. Many of us try to leave before we turn 18.” For the young, vulnerable and penniless, it is not uncommon for the journey to take two years. Once in Libya, Milka was held in a cell with hundreds of others for 10 months.

It is 4.22pm and already dark as Maëva Hammouche and Manon Berthou, a nurse and a midwife, both 25, continue their daily, 12-hour search for vulnerable girls through forests, swamps and industrial parks. Right now, they are at Rue des Verrotières. Although it has been dubbed “the new Jungle”, there are no visible tents or settlements, just a couple of battered white vans giving out hot food and tea.

Most people who stay in the safe house are minors. There is only room for six. Photograph: Alice Rowsome/The Guardian

Hammouche explains that when girls like Kidisti and Milka arrive in Calais, they are usually quickly paired up with a “brother” from Eritrea or Ethiopia. “These ‘brothers’ keep them ‘safe’, usually in exchange for sexual favours,” she says. “I ask them if they have a boyfriend; they say no. When I ask if they are sexually active, they nod. If I look at the number of condoms men ask me for, compared to the number of girls here, it does make me wince.”

They spot a young girl they haven’t seen before. “Looks like she’s got a ‘brother’ already,” says Hammouche. They introduce themselves using Google Translate. Sarah is 17 and from Ethiopia. She has been here for 10 days but has been too scared to come out from hiding in the forest until now. Hammouche and Berthou take her to their medical van, ask her more intimate questions, away from her ‘“brother”, tell her about the safe house and give her a sanitary kit (including a toothbrush, toothpaste, sanitary pads and baby wipes). Finally, they exchange numbers: “You can call at any time,” they insist. “Any time.” Sarah says she has a friend who is still too scared to come out of her tent. They hand her an extra kit.

“Stuck in tents, the girls can’t wash and often get vaginal infections. If it spreads to their face, it can become herpes. We often find them in quite terrible states because of the lack of basic hygiene,” Hammouche explains. “Some wipes will help.”

The following day, Sarah’s friend Hiba, who is also 17, is out under the watchful eye of her “brother”. It is bitterly cold and nearly all of the 22 girls currently sleeping rough in Calais want to sleep at the safe house. There is only space for six. Violaine makes some phone calls and finally convinces Secours Catholique, which runs a nearby shelter for homeless people, to take some of these women in. She drives them there, squeezing five passengers in her car at a time. Meanwhile, Hammouche and Berthou stay with the rest of them, crouched down in the mud, next to a small fire. It is pitch black. All the food vans are long gone. Five days ago, clashes, which they witnessed, left dozens of men in hospital. Are they worried? “We are here for the women regardless of the circumstances,” says Hammouche.

At 8.22pm, Violaine drives the last group to the safe house. As the volunteers walk in, they are bombarded with hugs and offers of tea. While the water boils, an illustrated guide to contraception is pulled out and discussed.

“If you have this implant in your arm, no baby. If you take a pill every day, no baby,” Hammouche begins. “But only a condom can protect you from infections like HIV/Aids,” she explains, pointing at an image of an erect penis. The girls explode in laughter, but listen carefully.

Later, they tell me why the girls were also so surprised by the illustrations of the female genitals. “A lot of them have been cut [female genital mutilation],” Berthou says. “We help give them access to reconstructive surgeries and often write up medical documents certifying they have been cut. It can help with their asylum cases.”

At 10.50pm, the pair are back at their own flat with Prel, Depierre and Violaine. Sitting around the table, eating chocolate, they chat about their day, sometimes making jokes that they tell me should not leave the flat. “It’s a survival mechanism,” Hammouche explains, wearily.

Dilva, seven months pregnant, showing the latest 3D scan of her baby. Photograph: Alice Rowsome/The Guardian

An hour later, the volunteers are all in bed, phones next to their pillows; they need to be on alert all night in case someone needs them. Meanwhile, Dilva is asleep in Grande-Synthe. Her ultrasound scan showed her that the baby was stable. She is desperate to reach her mother in Birmingham before giving birth, she tells me the next day, showing me the latest 3D scan of her baby boy. “There’s still some hope,” she smiles.

Midwives and “some hope” is all they have.

The names of the refugees have been changed to protect their identity.