EDD and siblings birthdays

[Elderlygrannygoat]

My friend thought she was late going into labour but gave birth nearly a week after her edd. This was on the same day of the month as her two year old toddler.
Do obstetricians take siblings birthdays into account when calculating the expected date of delivery?
I have noticed that many siblings have birthdates within two or so days of each other although maybe in different months.
eg my birthday falls on 24 July and my brother 21 March. My husband and his brother were born on the 31 of July and October respectively.
I could go on but perhaps other mothers have noticed this.
I suppose if your cycles are fairly regular, they reset to similar dates after birth. So subsequently you ovulate and give birth on the same days of the month?

Huh???

I meant same day of the month as her two year old toddlers birthday. Not that the toddler also gave birth! Doh!

Sorry I didn’t make that very clear!

I think I know what you mean but it doesn’t work like that. If you take an example of people having regular 28 day cycles... most months have 30/31 days so their period is not going to fall on the same dates of the months as time goes on. It may be the 18th one month, then the 16th, then 13th.

I’ m asking if other people have a similar experience of having sibling birthdays falling on close days of the month.
Perhaps as so few babies are born on their actual edds we have the 28 day cycle, 40 weeks birthdays a bit inaccurate.
Just asking for information at the moment. Think about the science after if it pans out.

None of mine share the same date all different days 17 18 22

From experience of birthdays in my family your theory absolutely doesnt fit.

I've never noticed this, and not sure how it fits with an average 28 day cycle. But I am one of three, two of us on the same date and one just two 'days' earlier (all different months).

Both of mine were born on the same day of the month but I think it's just coincidence more than anything because I don't know anyone else who shares 'same day of the month' birthdays with their siblings.

I am now thinking I am adopted as my three siblings are 23rd/24th/23rd even though different months. I am the 6th. I need to look into this My two DC are 6th and 4th I think you may be on to something here OP!!

I’m one of 4 (birthdays on 27th, 18th, 15th and 6th) so my mum definitely didn’t fit into your theory!

Dc1 was due 18/01, dc2 due 21/01.

I know lots of families who have siblings in the same month, so guessing a woman can be more fertile at a certain time of year? (April for me) If that's what you're getting at.

My friend had dc1 on 22/12 And dc2 22/02 (which happens to be her birthday too!).

Do obstetricians take siblings birthdays into account when calculating the expected date of delivery?

No, they don’t.

My three children all have different dates of the month to each other.

I don’t think this is a thing. I’m one of three, 16th, 17th and 27th.

DS was born on 10th and DC2 is due on 27th, so unlikely to be born anywhere near 10th.

There's only a maximum of 31 days in a month. It's not a very big coincidence for some families to have babies born on 2 or 3 consecutive numbers between 1 and 31.

You asked two qs in your OP.. one about whether obstetricians use your theory giving an edd, and one about whether we probably ovulate and give birth on the same day or similar days each month. I think I answered both with my post! But you then changed your q..
For your second post you asked for experience. I have two kids, born on the 14th and 15th of the same month. One was born two weeks late and the other 4 weeks early, both by induction. So nothing to do with my body clock!
And I’m one of 5 myself. Our birthdays are the 10th, 12th, 18th, 24th, 25th of different months.
Anecdotally and scientifically.. I don’t see it!

I have 2 with the same date, 1 the next day and then 1 2 weeks later. The only one who delivered close to my edd was the one on its own. I don't think it has any relation. Me and my siblings birth dates are all over a 2 week period.

Not the same thing, but similar scenario where two things happening on the same date (and you're only talking about the same day of the month which is far more likely) is the birthday paradox.

betterexplained.com/articles/understanding-the-birthday-paradox/

You only need 23 people in a room to have a 50:50 chance of 2 of them having the same birthday.

Me and my siblings were all born on 14/15th and dh and bil were both on 7th. None of my dc do that although dc4 and dc5 were both due on the same day but different years. I've been pregnant 8 times and 4 have been due late june/early july, 3 were due december/January and dc2 is the odd one out with a birthday in april. So I might be more fertile at easter and october. Although it could just be that we have more sex on the Easter bank holiday and when the clocks go back!

No, drs don’t take siblings birthdays into account when calculating a due date. With max 31 days in a month, it’s not surprising that many families have siblings with birthdays a few days apart.

Having said that, I’m one of four and our birthdays are 2nd, 15th, 20th and 29th. My kids are 15th and 30th.

Do obstetricians take siblings birthdays into account when calculating the expected date of delivery?

No. They don’t use tea leaves or palm readings either .

Thank you for the feedback.
I wish I was a statistician.
But would need several thousand replies I guess!
It was just a query I had after conversations with friends and family and I was puzzled by the coincidences.
I thought Mumsnet was the right forum to come up with the information .
Happy Christmas.

I have 2 children born on the same day (different year - not twins) and twins born on the same day. Other than that and looking at family's birthdates, your theory doesn't fit.

My dc's are 20 and 21st. I was given due dates of 22nd for both of them.

My dh and sil are 5/6th.

So we support the theory but I imagine it's just coincidence.

My 2 and DB’s 2 are 13, 14, 15 and 16th between them. Different months and years but easy to remember!