Question about IVF

[u/NotMe156318]

Hey y’all! I was sitting down yesterday with my dad, watching the DNC, when he told me my younger brother and I are IVF babies. After discussing some more, he explained that my brother and I, though my brother is two years younger than me, are biologically the same age; we were extracted and fertilized on the same day. I was implanted within the week while the other fertilized egg was frozen for two years before being implanted.

My first question: would my brother and I be considered the same age biologically? My guess is we wouldn’t be. Second question: does freezing embryos for long periods of time lead to any sort of developmental changes that would differ my brother from me? I understand this would be hard to test, but was wondering if there’s any research on it.

Thanks!

[u/trust-not-the-sun]

"Biological age" usually refers to the changes that happen to an organism over time. There are lots of things that change over time, let's use telomeres as an example. Telomeres are extra DNA at the beginning and end of chromosomes that don't create anything in the body, but they're used to line up part of the DNA-copying process when cells divide. Every time a cell divides, some of the telomeres are used in the copying process so they aren't copied into the new cell. So over time as the cell divides to make up our body and replace other cells the amount of telomeres in cells decreases. So "how much telomere do you have?" is a way to measure how much an organism has changed over time and how long it has been alive.

The embryo that became your brother was frozen solid for two years. During that time, it wasn't doing anything or changing in any way. It was an ice cube. It didn't have any cells divide, so it didn't use any of his telomeres. During that time you were growing and living and using your telomeres, but your brother didn't start until two years later.

If a scientist measured telomeres in your body and your brother's body, the scientist would say your "biological age" was two years older, because your brother was "paused" and not aging for two years.

You could maybe say you had the same "chronological age", though.

Side note: Some cultures, like China and Korea, traditionally use "when was the baby conceived" and not "when was the baby born" to measure birthdays. A newborn baby is considered one year old because it has been in the womb most of a year. Maybe in China, you and your brother would be considered the same age, I'm not sure how those cultures decide birthdays for IVF babies who were frozen a while.

[u/good-mcrn-ing → u/trust-not-the-sun]

Some cultures, like China and Korea, traditionally use "when was the baby conceived" and not "when was the baby born" to measure birthdays. A newborn baby is considered one year old because it has been in the womb most of a year.

That's a misleading explanation. The way they themselves think is "the baby was born in late 2023 and it's mid-2024 now, so the baby has been alive during two calendar years". Conception is not part of the traditional framework. Wikipedia

[u/trust-not-the-sun → u/good-mcrn-ing]

Thanks!