All iLive content is medically reviewed or fact checked to ensure as much factual accuracy as possible.
We have strict sourcing guidelines and only link to reputable media sites, academic research institutions and, whenever possible, medically peer reviewed studies. Note that the numbers in parentheses ([1], [2], etc.) are clickable links to these studies.
If you feel that any of our content is inaccurate, out-of-date, or otherwise questionable, please select it and press Ctrl + Enter.
Amniotic fluid pH during physiologic labor
Medical expert of the article
Last reviewed: 04.07.2025
The pH of amniotic fluid was studied in 160 women in labor during normal labor. The duration of labor in primiparous women was 12 hours 42 minutes + 31.7 minutes, in multiparous women 6 hours 05 minutes ± 4.85 minutes. The assessment of newborns according to the Angar scale was 7-10 points. In % of women in labor, pH recording began from the moment the amniotic fluid ruptured or the amniotic sac ruptured in the absence of labor.
To determine the pH value of amniotic fluid, the following groups were identified: 1st - no labor; 2nd - dilation of the cervix by 1-3 cm; 3rd - by 4-5 cm; 4th - by 6-8 cm; 5th - by 9-10 cm; 6th group - II stage of labor.
It has been established that the pH values of amniotic fluid are within the parameters characteristic of liquid biological environments of the human body. During the birth process, as labor progresses and the cervix opens, the pH value of the waters gradually decreases, indicating the depletion of their buffer capacity.
Thus, the pH of amniotic fluid in 6 groups was, respectively: 7.36 ± 0.005; 7.32 ± 0.008; 7.30 + 0.006; 7.27 ± 0.006; 7.23 ± 0.01 and 7.04 ± 0.04.
Intra-hour fluctuations in water pH: 0.02 ± 0.0005; 0.02 ± 0.0006; 0.019 ± 0.0007; 0.02 ± 0.0007; 0.03 ± 0.01.
The most significant decreases in pH values are observed at the beginning of labor, as well as at the end of the dilation period and in the second period of labor. Apparently, it is at these moments of labor that the fetus experiences increased loads, releasing acidic metabolic products into the amniotic fluid. Thus, in the 2nd group, the load on the fetus is associated with the transition of the uterus from a state of functional rest to a working mode, in the 5th and 6th groups - due to the movement of the fetus along the birth canal with compression of the presenting part. It should be especially emphasized that the small value of the average error of the arithmetic mean (M) indicates the stability of the indicators.
The value of intra-hour fluctuations in the pH of amniotic fluid was 0.02 and did not change during the process of dilation of the cervix. When calculating the criterion of reliability of the difference, no reliable differences were found between the studied groups, which indicates small deviations in the pH values of the waters from the average value during normal labor. The reliability of the difference in the pH values of the waters in the studied groups is as follows: the difference between the 1st and 2nd groups is reliable, between the 2nd and 3rd - unreliable, between the rest - a high reliability of the difference in indicators was found.
The greatest changes in the pH of amniotic fluid in the second period may indicate the maximum load on the fetus and correspond to the development of physiological acidosis in the fetus.
[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ], [ 8 ], [ 9 ], [ 10 ], [ 11 ]