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[Observations on serum and amniotic fluid hormone levels and ultrastructure of uterine myometrium before and during term labor].

OBJECTIVES
To evaluate the relationship between serum and amniotic fluid (AF) estradiol (E2), estriol (E3), progesterone (Po), cortisol (Co), human placental lactogen (hPL) concentrations and uterine contractions. To observe the ultrastructural changes of uterine myometrium before and during labor.


METHODS
Sixty-eight term-pregnant women (before labor 18, in normal labor 16, uterine inertia 34) were enrolled for study. Serum and AF E2, E3, Po, Co, hPL concentrations were measured by radioimmunoassay in 56 out of the 68 subjects. Myometrium gap junction (GJ), dense body (DB), sarcoplasmic reticulum (SR) were observed under electron microscope in the remaining 12 subjects (before labor 6, Uterine inertia 6).


RESULTS
(1) E2, E3 levels and E2/Po, E3/Po ratio in AF, but not in serum, increased successively in the groups before labor, in normal labor and uterine inertia with significant differences (P < 0.01). (2) Both serum and AF Co, hPL concentrations were significantly different before and during labor (P < 0.01, P < 0.05). (3) Serum E2, E3, Co and hPL levels elevated significantly in cases with uterine inertia after successful treatment with estradiol benzoate or oxytocin infusion. (4) Compared with the group before labor, the amount of myometrium GJ, DB, SR increased significantly after the onset of labor.


CONCLUSIONS
The elevation of serum and AF Co, hPL concentrations may be involved in the initiation of labor. This may be one of the major factors affecting the uterine contractions. Appropriate serum and AF estrogen (E), progestin (P), E/P ratio may be related to normality of uterine contractions during labor. The increase of GJ, DB, SR amount in uterine myometrium may be the histologic basis for the onset of labor.