Category Archives: The Science Stuff

Lies, damned lies and statistics

Going right back to the beginning of the pregnancy journey, there was a fascinating article on BBC News yesterday based on a new book (The Impatient Woman’s Guide to Getting Pregnant) about the sources for statistics used about conception and fertility rates.

A few key excerpts:

“Take this often-cited statistic: one out of three women over the age of 35 will not have conceived after a year of trying.

The data on which that statistic is based is from 1700s France. They put together all these church birth records and then came up with these statistics about how likely it was [someone would] get pregnant after certain ages.”

“A graph based on 17th-19thC birth records still features in the “Figures and Tables” section of the 2013 Nice fertility guideline”.

It amazes me even if it doesn’t entirely surprise me that some of the data being used to advise us is completely out of date. We worry about having children in our early thirties rather than late thirties when in reality there is no “cliff” when you turn thirty five that, as you blow out the candles on your cake, “poof” goes your fertility as well.

As the article mentions, if you actually use a more up-to-date study (Dunson et al, 2004) you find that the story is a lot more rosy for those in their late thirties with conception rates above 80% within a year. For those that are interested, I have included some more on the findings from the study at the bottom.

Because of the ethics involved in conception, pregnancy and birth, the ability to run true experiments where you can control factors is limited, the science becomes more like social science where you can’t control much if anything and just hope you can identify the main factors contributing to an effect (something the Chancellor will be wringing his hands about in the case of austerity economics!).

I guess the moral of the story is one drummed into me during GCSE History – know the reliability of your sources. If a statistic is making you change your behaviour then it is worth knowing where it came from, and judge for yourself its relevance. And if NICE are guilty of dubiously relevant statistics then anyone could be at it.

Trust no one Mr Mulder!

More from the Dunson et al 2004 study

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The graphs show the probability of falling pregnant for each age group cumulatively against the number of menstrual cycles they have been trying for. The difference between the first and the second graphs is that in the first, couples were having sex twice a week and in the second once (interestingly there is no graph for three times a week because they found no statistical difference between two and three times).

“The proportion of women failing to conceive within 12 cycles (thus meeting the criterion for clinical infertility) ranges from 8% for 19- to 26-year-olds to 13–14% for 27- to 34-year-olds, to 18% for 35- to 39-year-olds. If frequency of intercourse is reduced to once per week, the rates of infertility increase substantially to 15%, 22–24%, and 29% for women aged 19–26, 27–34, and 35–39 years, respectively”.

Like father, like son?

From the start, most people have said that Pip most resembles Mr Cath rather than me. There are exceptions: for example, my parents think he looks like me as a baby. And one friend who shall remain nameless recently commented that Pip looked like his father when he was born, but he is looking more and more like me “now that his cheeks are filling out a bit”. Um, cheers.

The funny thing is, it’s not just Pip, and certainly not just boys. Most babies really seem to look like their Dads. But why? Babies’ genes are split 50/50 so they should look like both their parents equally… but my experience and that of other people appears to suggest that this isn’t the case.

There are a few credible-ish theories as to why this might be:

1. Cavemen

Flintstone-family

One reason why babies look like their fathers could have its roots in evolution. To reassure the father that the baby is his own offspring, and therefore not a threat, this particular resemblance developed. As in the animal kingdom, it also discouraged the man from eating his young… possibly. The instinct to hunt and gather would also be stronger when one is providing for one’s own child.

2. A mother’s honour

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Breastfeeding as a method of contraception?

When we were in hospital, one of the midwives told us we (well really I) needed to go and see my GP to restart contraception (unless of course I fancied Irish twins) and that in the meantime I should not assume breastfeeding was an effective form of contraception. “Ha!”, we said, “Who would think it was?”, rather haughtily bracketing this with other old wives’ tale nonsense like that having a hairy baby will give you heartburn. But I did wonder at her telling us that and so finally looked it up and it seems I was wrong, breastfeeding can be an effective method of contraception: old wives 1, Elly 0 (well maybe I should give myself a point for having a hairy baby with no heartburn).
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My brown-eyed girl?

GCSE double science has a lot to answer for. It told me that if I found a blue eyed man and if we loved each other very very much and had a baby that with my blue eyes, two recessive genes would make a recessive gene and our babies would have blue eyes. Visiting Fred’s sisters as part of the grand baby parade, his sisters’ bet was on Elphie’s eyes turning brown from their current dark blue / slate colour – leading me to wonder, could they be right? Can two blue eyed parents produce a brown eyed kid? Had GCSE double science been fooling me all along?
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I needed to get an answer on this before Fred started questioning his parentage and looking strangely at the brown-eyed postman. Although in reality I think it should be the other way round – I can see definite signs of Fred’s features in her, she has his legs and feet (just the features a daughter wants from her father) and the dark colouring would seem to come from his side of the family, but where the signs of me are in the genetic mix are less clear. If she hadn’t done a stretch in my womb and come out of my ying yang, I would be the one questioning the parentage!

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You make me tongue-tied

For those who wondered where Monday’s post was, do not panic there was a post – I just managed to back to the future it and post it as if posted on Saturday, so it was there but very slightly hidden by the mists of time. So here it is, back in its rightful place – apologies for those psychologically scarred by the seeming absence of a post!

When Elphie made it back to her birth weight, I decided the time had come to breastfeed properly and move away from being a bizarrely-shaped bottle accessed via the nipple shields to mother-baby direct breastfeeding action.

So I went along to the breastfeeding drop-in session at the health centre. This was a regular weekly session run by a midwife / lactation consultant and like the Hotel California it seemed it was so good that once you’d gone once you would never leave due to the camaraderie and moral support provided by a group of mums getting together once a week and breastfeeding while quietly and informally sharing their experiences. Very nice it was too and plaudits to the NHS for providing such a thing.

When my turn came for attention from the midwife, I explained my problem and she examined Elphie and said that my problem was probably not flat nipples but more that Elphie was tongue tied. This surprised me as at least one of the midwives or health visitor who had come to our flat had checked for tongue tie and declared her untied. But it seems Elphie has the posterior type and that’s harder to spot.

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Got milk?

Many of you may be shockingly unaware that today is World Breast Milk Donation Day! This raises awareness for the practice of donating breast milk and milk banks in general.

I must admit that the existence of this had completely passed me by – my mammary glands being purely for show thus far rather than providing a useful milk producing purpose. It therefore took me a bit by surprise when someone I knew from school presented a picture on Facebook of her fridge full of bottles ready for donation.
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