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Standard, Population & Customised fetal size charts 9 – gender and parity

September 14, 2019

Customisation by fetal gender

After birth, male and female babies differ in size, and gender specific charts are widely used. This is reasonable since gender specific differences in mortality or morbidity are unrelated to fetal size.  On the contrary, male babies tend to be larger but have higher rates of mortality and morbidity, so gender specific charts are likely to better identify pathology.

There are also fetal gender differences in size (click here), so in theory gender specific charts might also be appropriate in utero.  However, in practice the gender differences are rather small, and because of practical difficulties – the ultrasonographer might be uncertain, or the parents might not want to know – gender specific fetal charts tend to be limited to specialist uses (click here).

Customisation by maternal parity

Birth weight and size increase with parity, at least over the first few pregnancies, but this is not independent of pathology. First babies are smaller than subsequent ones but have a higher mortality, partly because pre-eclampsia is common in first pregnancies, and partly because first labours tend to be longer. To a lesser degree, at least in the developed world, some of the increase in birth weight with increasing parity is related to increasing maternal weight. Again this is not benign. For these reasons customisation on maternal parity is unwise.

Tomorrow another technical digression. This time on estimated fetal weight (click here).

Jim Thornton


7 Comments leave one →
  1. Ann Roberts permalink
    September 14, 2019 9:00 am

    Got to disagree with this one. Do a poll on any parenting forum and you will find that some women have larger babies each time but some don’t. It’s a pernicious theory when applied to innacurate efw by ultrasound in second and subsequent babies. Just heard of a woman being advised elective CS because of previous good sized baby, just under 4kg so this one bound to be bigger? Previous sfvb. Efw by ultrasound at 37 weeks 9lbs 5oz, weight at C birth 10 days later 9 lbs exactly, just like the previous baby. She is finding recovery hard and painful compared with her previous vaginal birth, plus an older child to care for. Anecdotal, my four, first three all similar at 8lbs 13/14/12 oz, fourth was 8lbs8oz.


  1. Standard, Population & Customised fetal size charts 8 – height |
  2. Standard, Population & Customised fetal size charts 12 – WHO |
  3. Standard, Population & Customised fetal growth charts 14 – GROW |
  4. Standard, Population & Customised fetal size charts 16 – summary |
  5. Standard, Population & Customised fetal size charts 17 – addendum for twins |
  6. Jim’s growth chart navigator |

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