has been studied and in one case found to be absent from the fetus during the first trimester and present in fetal serum, urine, and AF in low concentrations during the second trimester. Cefazolin clearance from AF does increase during pregnancy, and is greater with polyhydramnios.422 The authors formulated dosing regimens to achieve appropriate AF concentrations of the antibiotic.
Hormones
Hormones and related metabolites have various origins and are present in measurable quantities in AF during the second trimester. Coelomic fluid contains high concentrations of progesterone, 17β‐estradiol, and 17α‐hydroxyprogesterone, which may be synthesized locally.423 Steroids other than progesterone are found in higher concentrations in coelomic fluid or maternal serum than in AF. Free diffusion of steroids across the amnion is limited, which may protect the embryo from unwanted exposure to biologically active steroids. Abnormal findings may be related to placental dysfunction, renal or adrenal anomalies or insufficiency, or specific endocrine disorders of the reproductive organs. Hormonal changes may also be linked to lipolysis or gluconeogenesis or to thyroid, parathyroid or pancreas malfunction. A list of the major hormone constituents is given in Table 3.4. Fetal and maternal tissues produce hormones that have effects on enzyme synthesis, membrane transport systems, and, not least, cyclic AMP. Measurement of steroid AF levels can be of some value in the evaluation of some pathologies, such as congenital adrenal hyperplasia and molar degeneration of the placenta.445, 446 Steroid concentrations from fetuses with Klinefelter syndrome were found to be normal.447, 448 Testosterone is elevated in the AF of male fetuses, although there is no significant increase of dihydrotestosterone.449, 450 Testosterone glucuronide used in conjunction with unconjugated testosterone was a good indicator for fetal sexing in AF451 but has been replaced by other methods (see Chapter 12).
Table 3.4 Hormones measured in amniotic fluid during the second or third trimesters
| Hormone | Approximate time of gestation (weeks) | Selected references |
|---|---|---|
| Aldosterone | 27 | 424 |
| Androstenedione | 14–22 | 425 |
| Annexin A5 | 15–24 | 380 |
| Apolipoprotein A | 16 | 214 |
| Apolipoprotein A‐I | Second trimester | 213 |
| Apolipoprotein A‐II | Second trimester | 213 |
| Apolipoprotein B | Second trimester | 213 |
| Apolipoprotein E | Second trimester | 213 |
| Cortisol | 13–24, 37, 38 | 426 |
| Dopamine | Second trimester | 323 |
| β‐Endorphin | 16–24 | 427 |
| Epinephrine | Second trimester | 234 |
| Erythropoietin | Second and third trimesters | 428 |
| Estradiol | 14–22 | 429 |
| Estrone | 14–22 | 430 |
| Estriol‐16‐glucuronide | 16 | 430 |
| Follicle‐stimulating hormone | 14–22 | 425 |
| Galanin | 38‐40 | 431 |
| β1‐Glycoprotein | 14–20 | 432 |
| Gonadotropin hCG | 15–20 | 432 |
| Gonadotropin LH | 16–20 | 433 |
| Growth | 17 | 426 |
| 17α‐Hydroxypregnenolone | 14–20 | 382, 434 |
| Insulin | 12–24 | 434 |
| Insulin‐like growth factor 2 and 3 | 12–20 | 435, 436 |
| Leptin | 14–18 | 437, 438 |
| β‐Lipoprotein | 16–21 | 439 |
| Progesterone | 14–22 | 429 |
| Prolactin | 15–20 | 440 |
| Prostaglandin | 15–40 | 441 |
| Relaxin | 9–40 | 355 |
| Renin | 16–20 | 330 |
| Testosterone | 10–22 | 442 |
| Thyroxine | 17–22 | 443 |
| Transthyretin | Third trimester | 444 |
| Triiodothyronine (T3) | 17–22 | 443 |
Levels of hepatocyte growth factor (HGF) are greater between 20 and 29 weeks of gestation than after 30 weeks. HGF was 300‐ to 400‐fold higher in amnion during the
