Must admit, as a pp said, unless I had had a really hard time trying to get pregnant, and trying for several years, I would be avoiding trying to conceive in March and April if possible. As a few other posters said, I have known a few people over the years who had December and January birthdays and they really hated it. (Moreso the people born in the second half of December and the first half of January.) Obviously the further away from Christmas it is, the better.
Like, I know 3 people with 23rd January, 27th January, and 29th January birthdays, and they say it's just far enough after Christmas to not be 'spoilt.' Ditto December... I know 2 people 7th December, and 9th December, and they say it's just far enough away. But the people I know born between say 15th December, and 10th of January did not like their birthday where it was, and wished constantly as a child that it was somewhere else in the year. (Indeed, a few of them wish it was somewhere else in the year as an adult...)
They either got forgotten by some people, OR got the dreaded 'joint Christmas/birthday gift.' So mean! If someone had a birthday in May, you wouldn't give them a Christmas present in December and say 'oh by the way, this is for your birthday on May 17th as well' would you?! So why is it OK to do it to a person who has a December/early January birthday?
Sometimes people have no choice! A friend of mine was only having one child ever, and her first born was a girl. (Born November 2016.) She and her daughter and DH were a little solid family unit, and were never having any more. (Had her at 29.) Then out of the blue, just after the little girl turned 3 years old, my friend discovered she was 5 months pregnant. No clue, still had periods, and couldn't remember ever missing a pill. (Put it down to a 2-3 day tummy bug later!) She kept the baby, another girl, who was born Christmas Eve 2019.
I think (and I could be making this up) that the majority of babies born in the 2 weeks leading up to Christmas day, and the 2 weeks after, are probably not planned (for that particular time...) I mean, most certainly wanted but not planned for around Christmas. I think most people in an ideal world would plan to have their baby between February and November if possible! (Just my musings!)