Take a look at the adults around you, and whether any of them have perfect proportions?<br><br>
Fortunately I had just read "The Genotype Diet" before I conceived, which talked a lot about different body types with very different proportions, and how these proportions are set in the womb with a combination of genetics and environment.<br><br>
And I had been sized for a custom bike a few years ago because all regular bikes hurt -- turns out I have a long torso and shorter legs, but all the shortness is in my lower leg and my femurs are actually long for my height.<br><br>
Daddy is also of interesting proportions: he's got the torso of somebody 6' tall, while he is 5'8". His inseam is shorter than men I've known who are 5'3". Right now the midwife is telling me the baby is very tall, based on the feel of him head-to-butt, but I think he's probably going to be of average total length with a long body.<br><br>
At our 20 week the dating was all over the place. The femur length made him older, something else made him seem younger. It turned out that the average (after taking every measurement twice) was pretty close (I know when I conceived), but individual measurements skewed it by a week or two either way.<br><br>
Even when individual measurements are consistent, the ultrasound dates can be off by a lot by that gestational age.<br><br>
Can you recall anything unusual around the dates you might have conceived? For me in retrospect I've been able to remember a day when I was EXTREMELY "in the mood" and, for lack of a better term, wet - mucous of an unusual consistency and abundance. Then, a day shortly after where I had pain (implantation) and spotting. Since it's your 6th maybe you recall some of these things that help you pinpoint your typical fertility cycle.
