Call the Midwife is known for tackling sad and serious issues, but season five is focusing on one in particular: Thalidomide. 

"The sense of responsibility with covering something so big and so important as Thalidomide was felt by everybody at all levels in the production," actor Stephen McGann tells us. 

"For the actors, it was very easy for us to see just how much this meant, how much care needed to be taken and everybody has to step up for that," McGann, who plays Doctor Turner, added. "We still feel that because with the theme of Thalidomide there is still more of the story to be unfolded."  

Thalidomide was a drug first marketed in the late 1950s as a sleeping pill but was prescribed to help nausea and morning sickness in pregnant women. The medication was later found to harm the development of unborn babies and cause serious birth defects, with over 10,000 children born with thalidomide-related disabilities worldwide in the early 1960s. 

Scenes involving babies with severe birth defects were "very emotional" to film, Emerald Fennell, who plays Nurse Patsy, tells us. But when it came to tackling the actual births of these babies affected by Thalidomide, there were practical issues to contend with too. "It's logistically quite complicated," she explains. 

Call the Midwife normally uses real newborn babies under 10-days-old (with pregnant mums being booked before they even go into labour) to film their birth scenes – lesions or wounds are added using the magic of CGI – but these births called for "a lot of moving prosthetics."

"It's quite complicated because we're doing something we haven't done before," Fennell tells us. 

"The prosthetics are great because they’re designed to weigh the same as real babies. They take a bit of getting used to because they look so real; you have that moment when you first see them and think it’s a real baby. You end up holding them like a real baby," she admits.

Creator Heidi Thomas shares Fennell's sentiment, revealing that they even named the prosthetic babies. "She was called baby Susan... They handed her to me and I just looked down at this little thing in the crook of my arm - and it did choke me, it really did," she told Radio Times earlier this year

"There are various degrees with the thalidomide prosthetics. Some have smaller limbs than others," adds Fennell. "They’re amazing because our makeup department operate them to make them breathe. It’s very moving and sort of awful to see because they really do look like real babies. All the art department have been amazing." 

When it came to Thalidomide, it was important for the show to strike a balance between upsetting and uplifting moments, says Fennell: "People went on to live amazing lives as campaigners and have rich family lives, so we’re very careful to show that it’s a bad thing, but good can come out of it. It’s a bittersweet balance." 

Whatever Call the Midwife has achieved so far this series, they seem to be getting it right, with last Sunday's episode drawing in over 7.5 million viewers. When it comes to reactions from fans, McGann reveals that the cast and crew have "been overwhelmed" too.

"We are very lucky, we are very privileged, very fortunate that we can do this to such a big audience," he says.