Doing the maths

Folks who follow our other blog may remember a little incident with DH's kidneys when we were applying for our resident's visa a while ago. We had to undergo some medical check-ups and one of the things they checked was our urine.
Well, DH's results at the time came back abnormal, he was suffering from 'kidney failure', we were told by the Dr. That was the strangest thing ever: DH wasn't aware at all that he had troubles with his kidneys, the whole family got stressed, and besides that these results brought our stay in NZ in jeopardy.
These things always happen in the festive season, so in the middle of the X-mas holidays while we had friends staying with us he had to collect his urine in a huge container, can't remember if it was for 48 hours or a whole week :-)

Anyway, we got his results on a sheet of paper and as we are good with numbers and formulas (DH) and quite good at finding evidence from research on all sorts of things (me), combining these lovely skills you'll get us questioning medical results. In the case of DH's 'kidney failure' we found out that some moron had made a mistake with the very complicated formula and that DH never could have had these results. Only from the age of 86 years would it be possible. So no kidney failure for DH!

Now I'm going to translate this to our pregnancy - no miracle stories, I'm sorry, but still....
Again we found a mistake in the latest scan measurements, which has consequences for the use of the formula to estimate baby's weight, and which means the difference between showing a total standstill in growth or some growth, which in turn may mean the difference between actively interfering in the pregnancy or applying a 'wait and see' policy.

Interesting is some research into the formulas they use to estimate baby's weight. There are numerous formulas in use, and they all result in a different outcome. The perfect formula hasn't been found yet. We checked a few of those formulas with the measurements from our scans, taking the error out, and the most pessimistic formula tells us that baby is currently weighing 240 grams, and the one we like most is the formula saying that baby is 320 grams. The one they used at the hospital and has the measurement error in it says baby currently weighs 200 grams.

Estimating baby's weight is interesting, but also prone to inaccuracy as those formulas are based on average babies at the end of a normal pregnancy, so what we also did was plotting all our scan results thus far on fetal growth percentile charts. That makes visible whether there has been growth at all, and how baby is doing compared to the general average. See below for a chart related to the diameter of baby's head.

What we achieve with this? Hmm, not much really, but we feel a lot better informed, the picture is a bit less gloomy than it was, and it emphasised our decision to 'wait and see'. You never know.
And our midwife will slam the hospital around the ears because of the measurement error :-)

What the error was? Inaccurate use of cm's instead of mm's. Which made the circumference of the head 17.3 mm instead of 173 mm and thus a lot smaller than the diameter of the head, which was 50mm. And that is impossible.