The ratio of fetal weight to placental weight tends to increase with increasing gestational age.
fetal-to-placental ratio =
= (weight of fetus in grams) / (weight of placenta in grams)
week gestation |
F/P ratio low |
mean F/P ratio |
F/P ratio high |
23 |
3.96 |
4.44 |
4.92 |
24 |
3.61 |
3.7 |
3.79 |
25 |
3.88 |
4.01 |
4.14 |
26 |
3.43 |
3.91 |
4.39 |
27 |
4.53 |
4.94 |
5.35 |
28 |
4.59 |
5.34 |
6.09 |
29 |
4.38 |
4.91 |
5.44 |
30 |
4.98 |
5.65 |
6.32 |
31 |
4.55 |
5.11 |
5.67 |
32 |
4.85 |
5.41 |
5.97 |
33 |
5.88 |
6.39 |
6.90 |
34 |
6.18 |
6.53 |
6.88 |
35 |
6.15 |
6.54 |
6.93 |
36 |
6.59 |
6.89 |
7.19 |
37 |
6.59 |
6.93 |
7.27 |
38 |
7.22 |
7.37 |
7.52 |
39 |
7.41 |
7.52 |
7.63 |
40 |
7.59 |
7.68 |
7.77 |
41 |
7.34 |
7.53 |
7.72 |
42 |
7.13 |
7.36 |
7.59 |
43 |
7.77 |
7.9 |
8.03 |
Initial line approximations:
F/P ratio low =
= (0.0004863 * ((week gestation) ^2)) + (0.1952285 * (week gestation)) -1.342432
F/P ratio high =
= ( - 0.0057 * ((week gestation)^2)) + 0.57497 * (week gestation) - 6.175338
Subsequent line approximation for the mean ratio:
mean ratio for gestational age =
= (-0.002618 * ((week)^2)) + (0.3851 * (week)) - 3.759
Specialty: Obstetrics & Gynecology, Pedatrics