I found out I was pregnant two days after my husband, Joe, and I had signed up to run the 2011 Chicago marathon and each paid the $145 (£113) entry fee.

It was my second pregnancy and would be my eighth marathon. My PB was 3hr 25min, so I wasn’t an elite runner, but I took it very seriously. Running has always been a huge part of my life and I ran a lot during my first pregnancy. This time, though, I was pretty sure that I wouldn’t take part in the race. My first baby, Caleb, was born three weeks early, and this one was due to arrive a week after the marathon, so I assumed that I’d have had it by then anyway.

I was 27, healthy and there were no complications with the pregnancy. My doctor said it was fine to keep exercising. I continued to train, never pushing myself. The week before the marathon, I managed comfortably to run 13 miles.

The night before, when the baby still hadn’t shown any signs of arriving, I thought I could probably start the race and see how I felt. My doctor had advised against running for the entire 26.2 miles, so I planned to run a bit and walk a bit and take it nice and easy. I wasn’t interested in breaking any records.

The day of the race, 9 October, was beautiful; warm, but not uncomfortably hot. My parents came to cheer us on and look after Caleb. Everybody was supportive of my decision; no one tried to dissuade me or questioned whether I should do it so near my due date. I knew my body: if anything hadn’t felt right, I wouldn’t have gone ahead. I was full term, so I knew if I were to go into labour, it was a healthy time for that to happen.

Joe and I set off together. We took it very easy. Going so much slower than usual made it different from any marathon I had run before. Normally, I go into a zone and I’m not aware of my surroundings, but I found this run fun and relaxing. I got to see the city and enjoy the crowd. I never hit the wall.

By mile eight, however, Joe was flagging. He hadn’t done much training and the heat was getting to him. He began to walk and slipped behind. I had a few blisters, but otherwise I felt great, so I continued. The crowd were really supportive when they saw me. Obviously, I stood out. I had lots of people cheering me on, shouting, “Go, pregnant lady!”

I had gone in with no expectations, but I felt good, so I just kept going. I passed the finish line with a smile on my face. My time was 6hr 25min 50sec. Joe arrived 19 minutes after me, delighted that we had both finished.

About 30 minutes later, we were sitting in a grassy area when I felt contractions. They didn’t feel like Braxton Hicks. We decided to go to the hospital. I didn’t know how much time we had; I knew I would rather get something to eat and get there in good time than go home to take a shower.

I was still in all my running gear. We told the nurses we had just come from the marathon and that I had finished the race. I’m not sure they believed me.

The birth was straightforward and took about four hours. June was born about 10.30pm. I couldn’t believe that it had all happened on the same day – it was the longest day of my life. On reflection, giving birth is definitely harder than running a marathon. Give me a marathon any day. After all that, I should probably have been exhausted, but I wasn’t able to sleep.

June is now almost six and starting to understand what happened that day. A couple of years ago, we were talking about how someone had given birth, and June said, “Did she run a marathon, too?” Hopefully, she won’t always think that you have to run 26.2 miles in order to have a baby.

I still love running and try to do at least one marathon a year. My next challenge is to take part in a 100km race. I’ve since had a third baby, and if any of the kids are going to be runners when they are older it is June. Not that I’m going to push her, but she clearly has it in her blood.

• As told to Sophie Haydock.

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