When I missed two periods ten years ago I was caught up in a new romance. I was 23, in my first media job and still getting to know Daniel, a university student. When a doctor at the family planning clinic asked how I felt about being 15 weeks gone, I felt shocked, but not particularly emotional. I refused to associate a baby with this unwanted pregnancy.

Daniel offered to support me, but I didn't want to be a mother yet. I spent the next day calling abortion clinics. I didn't tell my family, not even the person I usually turned to: my stepsister.Jane is seven years older than me. While I was accidentally getting pregnant, she and her husband, Nigel, were enduring their first IVF cycle. They'd been trying to have a child for three years, but there was a problem with Jane's Fallopian tubes. It would be insensitive to tell her. Plus, I didn't want her to talk me out of it.

I avoided her calls during the seven-day wait for the operation. When I discharged myself I was still having contractions. I didn't want to stay at the clinic a second longer. I was in pain, physically, but emotionally numb. I resolved to tell my family one day, when Jane had her own baby.

That Christmas I took Daniel out to meet my family. Jane broke down in the pub toilets. Her second cycle of IVF had failed and her marriage was collapsing. As she opened her heart, I deeply regretted not being honest, as she was with me.

I fantasise about murder to save my marriage

A woman in her fifties speaks of the torment caused by her deceitful but charming 72-year-old husband’s affair with a carer

Background

• I used to have sex with my brother

• I hoped bulimia would make me beautiful

• Family secrets: the grief for my illicit love

• I wish I had married for money, not love

• My mother hated all women

Over the next five years Jane divorced Nigel and I married Daniel. My guilt made it impossible to feel comfortable in Jane's company. I dreaded seeing her. Splitting with Nigel had scuppered her plans to have a family, and the man she was dating had three children with his ex-wife. Jane constantly said how unfair it was that other women fell pregnant easily. Every friend's pregnancy was a betrayal, and my secret abortion was the most duplicitous act of all.

After marrying, Daniel and I were ready for a family. “At least you know you can get pregnant,” Jane said coolly when I miscarried. The loss devastated us, and I finally understood the agonising disappointment Jane felt. My next pregnancy was successful. I conceived the month after the miscarriage and my apparently abundant fertility was too much for Jane. She e-mailed saying that my pregnancy was too difficult to cope with. I respected that.

In the 16th week of my pregnancy, I finally faced up to the implications of my termination. I longed for my baby to be born safely, and grieved for the unborn child I'd rejected so easily. When my boy was born Jane visited us in hospital. I was terrified that she'd glance at my notes and see the incriminating evidence; pregnancies, three, live births, one. Watching her gaze adoringly at my son was humbling. I didn't feel that I deserved to be a mother.

In the same circumstances I would make the same decision again, but not so lightly. I've wondered if I should have given Jane the baby. But life's not that simple. Jane is 41 now, and there is little chance she will conceive naturally. She remarried and is focusing on being a stepmother. Our contact has withered. I feel unworthy of her friendship. My guilt, my secret and the fact that I'm a mum and she is not have become an insurmountable barrier.

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