Dr. Peterson measured Conner's CRL (crown-rump-length) to be 32 cm, and his CHL (crown-heel-length) to be 48 cm. CRL is nearly the shortest length the baby can be in the uterus when it is in fetal position.
Dr. Peterson measured Laci's uterus to be 23 cm, from the top of the fundus to the bottom of the cervix where it attaches to the vagina. Normally, a baby doesn't occupy any part of the cervix until it descends in preparation for birth.
For my expert witness that a 32 cm CRL could not be housed in a 23 cm top-to-bottom uterus, I call Dr. J. Clifton Edgar, author of The Practice of Obstetrics, published in 1916 as a textbook for midwives. Dr. Edgar will provide us with a chart which gives the size of the fetus and uterus at the different stages of pregnancy. Edgar derived his statistics and data from 2200 confinement cases he observed: 1000 from the New York Maternity hospital and 1200 from the Mothers' and Babies' Hospital. That is not the sum of his experience, however, as he had personally observed over 20,000 confinements by the time the 5th edition of The Practice of Obstetrics was published in 1916.
Dr. Edgar's expert testimony includes the CRL and CHL of fetuses compared to the 3-dimensional measurements for the uteri from which they came. Many expert sources give us the age of fetuses based on CRL, CHL, or the measurements of one or more bones, but Dr. Edgar is unique in that he gives us the 3-dimensional measurements of the uteri that housed those fetuses. Some who steadfastly resist any evidence that Scott Peterson is factually innocent argue that since the uterus is 3-dimensional, it can be shorter than the CRL of the baby. However, when we look at the 3-dimensional measurements of the uterus as provided by Dr. Edgar, we see that without fail the uterus' longest measurement is always longer than the CRL of the fetus. That's because the uterus is holding more than just the fetus. The placenta is often 1/3 the size of the baby, and then of course there is the amniotic fluid that takes up some of that 3-dimensional space.
Dr. Edgar informs us that Dr. Peterson's 48 cm CHL matches the maximum CHL for 9 months, which is what Peterson estimated Conner's age to be.
Dr. Edgar informs us that a 32 cm CRL fits in with the 10th month range.
Pointing specifically at the uterus size for the 9th month, Dr. Edgar notes that we see, in centimeters, 32.50 x 23.25 x 21.25. 32.50 cm - 23 cm for Laci's uterus = 9.5 cm difference, or 3.7 inches.
Dr. Edgar also informs us that the uterus size for 8 months, or 32 weeks, which was Conner's gestational age on December 23, is 28.75 x 21.25 x 17.5. 28.75 cm - 23 cm for Laci's uterus = 5.75 cm difference, or 2.3 inches.
In Dr. Edgar's expert opinion, a 32 cm CRL (48 cm CHL) fetus cannot be housed in a 23 cm top-to-bottom uterus.
Anyone may obtain Dr. Edgar's book from Google Books, entirely free.
If anyone wants to check Dr. Edgar's fetal sizes against "modern" measurements, you can use this chart. You will see that Dr. Edgar's fetal measurements for each age are right in line.
One final note. Laci had her last prenatal appointment on the afternoon of December 23. No abnormality was observed in either her fundal height or Conner's development.