The state of bone and mineral metabolism in underweight pregnant women

Materials and methods. The research included 41 pregnant women with body weight deficiency at the beginning of pregnancy and 37 of them before labor, and also 35 pregnant women with normal body weight. The content of total calcium, nonorganic phosphorus, parathyroid hormone, osteocalcin, vitamin D total (25(OH)D) were defined in blood serum. The study of bone tissue mineral density was held with the use of ultrasound densitometry.

Состояние костно-минерального метаболизма у беременных женщин с дефицитом массы тела In the available literature there are various data about the changes in calcium-phosphorus metabolism and bone metabolism during pregnancy.Some authors note the decrease of total calcium level in blood serum with increase in the term of pregnancy [1,2].There are different points of view about ionized fraction of calcium during pregnancy: its decrease, no changes or gradual increase during pregnancy [1][2][3][4].The researches have [5,6] revealed the increase in blood serum calcitriol concentration during pregnancy and insignificant changes of parathyroid hormone level (PTH).There are different data that the decrease of mineral density of bone tissue is diagnosed in 27 % of examined women.Due to the fact that among the causes of bone tissue metabolism affection progress in pregnant women the body weight deficiency plays the significant role as the result of alimentary factor, in particular insufficient consumption of protein, calcium, vitamin D with food [7,8], it is actual to conduct the researches that have the aim to study bone and mineral metabolism in underweight pregnant women.

Aim
To study the state of bone-mineral metabolism in underweight pregnant women.

Materials and methods
The research included 41 pregnant women with body weight deficiency (BWD) at the beginning of pregnancy (8-10 weeks).Due to spontaneous abortions and premature delivery the repeated laboratory tests before delivery (36-38 weeks) were held for 37 women.Also 35 pregnant women with normal body weight (NBW) were examined.The body weight deficiency was defined according to WHO recommendations (1997) on body weight index.
To find out the total calcium in blood serum the following methods were used: the colorimetric method, nonorganic phosphor -spectrophotometric, parathyroid hormone (PTH), osteocalcin and vitamin D (25(OH)D) total -immunochemical with electrochemiluminescent detection (ECLIA) with usage of test-system Roche Diagnostics (Switzerland) on Cobas analyzer 6000 (with 501 module) of Roche Diagnostics (Switzerland).
The examination of bone tissue mineral density was carried out with the usage of ultrasound densitometric apparatus Omnisense 7000.According to recommendations of World Health Organization the examination of bone tissue state was made on T-criterion which reflected the deviation from peak values of bone tissue mineral density in young healthy women.
The processing of statistical information data was carried out with the usage of software SPSS Statistics17.0.As the majority of variables didn't correspond to normal distribution, they were represented by median (Me) and interquartile range -25 and 75 percentile (25; 75 %).The comparison of quantitative data of two independent groups was made with the help of Mann-Whitney U test.Comparison of quantitative data of two associated groups was carried out with the help of nonparametric Wilcoxon signed rank test at the beginning of pregnancy and before labor.95 % confidence interval (CI) using Wilson's method was defined to the frequency.Spearman's rank correlation coefficient (r s ) was calculated to define strength and direction of interconnection between variables and as well as 95 % CI.The comparison of quantitative features was done with the help of two-sided Fisher's exact test.
The referential ranges of calcium, phosphorus and bone tissue markers given by the laboratory do not consider the condition of pregnancy.It is stated that ranges of total calcium were less than referential at the beginning of pregnancy in 8 women out of 41 women with BWD (19.5 %; 95 % CI: 10.2-34.0%) and in 1 out of 35 with NBW (2.9 %; 95 % CI: 0.6-13.2%), the statistical significance between indexes was noted (P = 0.033), before delivery the amount of these
Whereas studying of nonorganic phosphorus content in blood serum revealed that despite the body weight its concentration in the pregnant women was within norm.At the same time the decrease in its level was noted before delivery (BWD from 1.18 (1.12; 1.24) up to 1.16 (1.08; 1.21) mmol/l; Z = -3.1,P = 0.002; NBW from 1.21 (1.17; 1.29) to 1.20 (1.14; 1.25) mmol/l; Z = -3.2,P = 0.001).Also there was stated statistically considerable decrease of indexes in BWD women in comparison with NBW women (at the beginning of pregnancy -U = 502, Z = -2.3,P = 0.024; before delivery -U = 451, Z = -2.2,P = 0.027), but this difference was less expressed than in ranges of total calcium (Fig. 1).
As it has been mentioned earlier there were no referential ranges for the pregnant, already at the beginning of the pregnancy in 11 women out of 41 with BWD (25.8 %; 95 % CI: 15.7-41.9%) the level of PTH was lower than normal standards, whereas in NBW woman it wasn't gone beyond the standards.During pregnancy the concentration of PTH
At the study of vitamin D status during pregnancy it was found out that its changes in BWD women were the same.At the beginning of pregnancy its rates were 27.1 (24.1; 30.0) ng/ml and at the end of pregnancy they decreased up to 23.8 (20.5; 27.8) ng/ml (Z = -4.7,P < 0.001) ant the same was typical for women with NBW -29.9 (27.8; 33.3) and 28.0 (25.8; 29.9) ng/ml (Z = -2.3,P = 0.024) respectively.Although the difference between the indexes in both groups had statistical ranges in BWD women it corresponded to the maximal ranges.In BWD pregnant women lower levels of vitamin D were found, which got verse with the pregnancy term increase, that is seen from the difference between groups BWD and NBW at the beginning of pregnancy (U = 439, Z = -2.9,P = 0.004) and before delivery (U = 310, Z = -3.8,P < 0.001).The positive thing is that the level of vitamin D wasn't gone beyond the referential standards in patients.

Conclusions
1.The course of pregnancy in women with BWD is accompanied by the affection of bone-mineral metabolism, that is seen from statistically considerable decrease in total calcium, phosphorus, PTH, osteocalcin and vitamin D indexes.
2. At the beginning of pregnancy 36.6 % of women with BWD have signs of osteopenic syndrome which is statistically much oftener than in women with NBW (5.7 %, P = 0.003).Before delivery the number of the pregnant wom- Horizontal lines -referential ranges.

Original research
en with osteopenic syndrome increases up to 51.4 % among women with BWD and up to 11.4 % among women with NBW (P < 0.001), the relative risk of osteopenia in the BWD pregnant women is 4.5 times higher (95 % CI: 1.7-11.9).Prospects for future scientific research.Due to the fact that dismetabolism in BWD affects the bone-mineral metabolism and leads to obstetric complications, it is necessary to start their prevention from renewal of bone tissue function and its protection.The understanding of this problem determines that the osteoprotective medicines inclusion into treatment and preventive measures is highly necessary.

Fig. 3 .
Fig. 3. Content of bone tissue markers in women with BWD and NBW.
Correlation interconnection between concentration of total calcium and nonorganic phosphorus.