**6.1 Amniotic fluid production**

The essential function of AF is to cushion the fetus (Williams et al. 1980). The fluid gives the fetus space to grow, and allows it to undergo a `physical´ development. The AF function is also to protect the fetus from trauma and to maintain temperature. It also has a minimal nutritive function.

Lactate Level in Amniotic Fluid, a New Diagnostic Tool 231

No major improvement has occurred in the diagnostics of dysfunctional labor since the introduction of the "partogram" by Friedman and Philpot in the 1970´s. Dysfunctional labor is still one of the leading obstetrical problems, worldwide. About 20% of all deliveries have

Dysfunctional labor is according to WHO defined as "a clinical deviation from expected progress" (no dilatation of cervix by 1 cm/hour, or no progress in 2 hours).The partogram is recommended to be used in all deliveries. Dysfunctional labor involves a long and painful delivery. The woman is in active labor, but the delivery progress ceases and the dilation of cervix does not proceed. The fetus does not pass through the birth canal, and the delivery comes to a halt. The reason behind dysfunctional labor is very little known, and several facts

A prospective observational study was performed at Dept of Obstetrics and Gynaecology at South General Hospital, Stockholm, Sweden in 2002-2004 (Wiberg-Itzel et.al 2008). 75 women with a healthy and normal pregnancy and a spontaneous onset of labor were included in the study. AF was collected from an intrauterine pressure catheter and analyzed blinded every 30 minutes during the active phase of labor. The result was then related with the obstetrical outcome (spontaneous vaginal or operative delivery due to dysfunctional labor). The results showed that a high level of lactate in the amniotic fluid (>10.1mmol/l) at two consecutive measure during the active phase of delivery, had a strong association with

A second prospective observational study was carried out at the same hospital in Sweden between 2006-2008 (Wiberg-Itzel et. al 2010). AF from 850 healthy, normal deliveries was collected at every vaginal examination during labor. The samples were analyzed blinded. The purpose of this study was to evaluate if the level of lactate in amniotic fluid, together with the partogram recommended by the WHO could improve the diagnostics of an arrested labor. The study showed that the combination of the level of lactate in amniotic fluid and the partogram gives an improved tool to handling a delivery if there is a halt in labor progress. Among the women who was included in the study and delivered operatively due to dysfunctional labor, over 80% had an increased level of lactate in amniotic fluid (>10.1mmol/l) when labor arrested. The duration of labor was also

Is there an unknown transport of lactate from the uterine tissue to the AF? Experimental studies with the purpose of finding an explanatory model for the transportation of lactate out of the myometrium and into the amniotic fluid have been performed (Akerud et.al 2009). Biopsies from uterine muscle, amniotic fluid samples, umbilical cord blood and biopsies from placenta of 60 women delivered by caesarean section were collected. The presence of lactate carrying protein was identified by immunohistochemical analysis. The proteins MCT1 and MCT4 were for the first time identified in human uterine tissue. MCT1 was found in all samples but MCT4 was found only in samples from the group of women that were diagnosed as having a dysfunctional labor. The MCT transport proteins bring lactate from uterine tissue to AF, and MCT4 is activated only in dysfunctional labor with a hypoxia of the tissue. Studies are underway to examine whether there are more systems for

prolonged within the group of women with an elevated lactate level in AF.

**7. Lactate in AF, a new diagnostic tool in labor** 

been shown to have an abnormal labor progress.

are probably due to a dysfunctional labor.

transport of lactate in myometrial tissue.

the diagnosis of dystocia.

In the first half of pregnancy AF has a composition similar to fetal extra cellular fluid. The volume is closely related to fetal weight, and the skin of the fetus offers no resistant to movement of fluid. AF at this stage may be regarded as an extension of fetal extra cellular fluid. Beyond midpregnancy (about 20 weeks) the fetal skin keratinizes, and continuity between the fetal extra - cellular fluid and AF is lost. AF becomes completely external in the sense that it can now no longer equilibrate with either the fetus or the mother. After keratinisation of the fetal skin, the AF osmolarity decreases. A part of the changing composition reflects the increasing maturity of the fetal kidneys. The fetal kidneys begin to produce urine at about 12 weeks of gestation. Low osmolarity provides a large potential osmotic force for the outward flow of water across the intra- and transmembraneous pathways.

The regulatory mechanisms to achieve an adequate AF volume operate at three levels; placenta control of water and solution, transfer regulation of inflow and outflow by the fetus, and maternal effects of the fetal fluid balance. The most contributing proportion of the AF balance is the fetus and its urine production, and the AF ingested by the fetus through swallowing. A smaller contribution of AF is distributed by the fetal pulmonary fluid production, and fluid filtering through the placenta and the membranes.

The volume of amniotic fluid each week of gestation is quite variable. In healthy pregnancies the AF volume has its maximum at 32-34 weeks, averaging 800 ml. Thereafter it declines, and the decline will be most marked post term.

Fig. 3. AF volume as a function of gestational age. Dots represent measured volumes with 2 week intervals (mean) in 705 women. Shaded area represents 95% confidence interval. (From: William's Obstetrics 21st edition, 2001).

In the first half of pregnancy AF has a composition similar to fetal extra cellular fluid. The volume is closely related to fetal weight, and the skin of the fetus offers no resistant to movement of fluid. AF at this stage may be regarded as an extension of fetal extra cellular fluid. Beyond midpregnancy (about 20 weeks) the fetal skin keratinizes, and continuity between the fetal extra - cellular fluid and AF is lost. AF becomes completely external in the sense that it can now no longer equilibrate with either the fetus or the mother. After keratinisation of the fetal skin, the AF osmolarity decreases. A part of the changing composition reflects the increasing maturity of the fetal kidneys. The fetal kidneys begin to produce urine at about 12 weeks of gestation. Low osmolarity provides a large potential osmotic force for the outward flow of water across the intra- and transmembraneous

The regulatory mechanisms to achieve an adequate AF volume operate at three levels; placenta control of water and solution, transfer regulation of inflow and outflow by the fetus, and maternal effects of the fetal fluid balance. The most contributing proportion of the AF balance is the fetus and its urine production, and the AF ingested by the fetus through swallowing. A smaller contribution of AF is distributed by the fetal pulmonary fluid

The volume of amniotic fluid each week of gestation is quite variable. In healthy pregnancies the AF volume has its maximum at 32-34 weeks, averaging 800 ml. Thereafter it

Fig. 3. AF volume as a function of gestational age. Dots represent measured volumes with 2 week intervals (mean) in 705 women. Shaded area represents 95% confidence interval.

production, and fluid filtering through the placenta and the membranes.

declines, and the decline will be most marked post term.

(From: William's Obstetrics 21st edition, 2001).

pathways.
