Serum is the clear liquid that can be separated from clotted blood. Serum differs from plasma (which is the liquid portion of normal unclotted blood containing the red and white cells with platelets). It is the clot that makes the difference between serum and plasma.
Pregnancy which is the carrying of one or more offspring, known as a fetus or embryo inside the womb of a female is a physiological stress in which many changes occur in the milieu interior of the body (Kashinakunti et al., 2010). Lipid metabolism changes during pregnancy; this is caused by maternal hormonal changes. Pregnancy is often defined as beginning when the developing embryo becomes implanted into the endometrial lining of a woman's uterus. Normal pregnancy takes about 38-40week. Pregnancy is typically broken into three periods, or trimesters (called first, second and third trimester) each of about three months (The American Heritage® Dictionary of the English Language, 2000).
The first 12 weeks of pregnancy are considered to make up the first trimester. During this period the nipples and areolas darken due to a temporary increase in hormones. Morning sickness is another event that occurs in about seventy percent of all pregnant during first trimester (World Health Organization, 2001)
Weeks 13-28 of the pregnancy are called the second trimester. Most women feel more energized in this period and begin to put on weight as the symptoms of morning sickness subside and eventually fade away. In the 20th week, the uterus, the muscular organ that holds the developing fetus, can expand up to 20 times its normal size during pregnancy.
In the third trimester, the fetus grows most rapidly during this stage, gaining up to 28 g per day. There is also head engagement in the third trimester, that is, the fetal head descends into the pelvic cavity so that only a small part (or none) of it can be felt abdominally. Week 28-40 are called third trimesters.
During pregnancy, women undergo many physiological changes, which are entirely normal, including cardiovascular, hematologic, metabolic, renal and respiratory changes that become very important in the event of complications. The body must change its physiological and homeostatic mechanisms in pregnancy to ensure the fetus is provided for. Increases in blood sugar, breathing and cardiac output are all required. Levels of progesterone and oestrogens rise continually throughout pregnancy, suppressing the hypothalamic axis and subsequently the menstrual cycle.
Change in lipid profile has been observed to vary with gestational age and also at different period or trimesters of pregnancy but the most significant change in lipid profile occurs at second and third trimester of pregnancy.
The lipid profile is a group of tests that are often ordered together to determine risk of coronary heart disease. They are tests that have been shown to be good indicators of whether someone is likely to have heart attack or stroke caused by blockage of blood vessels or hardening of the arteries (atherosclerosis). The lipid profile typically/ majorly includes:
- Total cholesterol (TC).
- High-density lipoprotein (HDL), often called good cholesterol.
- Low-density lipoprotein (LDL), often called bad cholesterol.
- Triacylglycerol (TG).
Very Low-Density Lipoprotein and Non-HDL might sometimes be included
Total cholesterol
Cholesterol is a waxy steroid or fat that is manufactured in liver or intestine. The name cholesterol originates from Greek words; chole-(bile), stereos-(solid) and ol- alcohol. It used to produce hormones especially steroid hormones like aldosterone, cortisol, testosterone, oestrogen e. t. c (Emma. 2009). It is also required to build and maintain membrane, it modulates cell membrane fluidity. Cholesterol is recycled and excreted by liver via bile into the digestive tract. Dietary sources include cheese, egg, beef, pork and also in human milk. Total cholesterol (TC) is considered normal when it is less than 200mg/dl, borderline high was between 200-239 mg/dl and considered high when it is greater than 240mg/dl.
The serum cholesterol concentration increases progressively throughout gestation. On average, mean cholesterol increases by 40% during gestation (Martins et al., 1999). Hypercholesterolemia is a key factor in the pathophysiology of atherosclerosis (Igweh et al., 2003).
TRIACYLGLYCEROL (TAG/ TG)
They are esters derived from glycerol and three fatty acids, main dietary sources are from vegetable oil and animal fat (CBN, 2007). They are the major component of very low density lipoprotein (VLDL) and chylomicrons, they play important role in metabolism as source of energy and transporter for dietary fat. They are also called triglyceride. Triglyceride is also considered normal when it is less than 150mg/dl, borderline TG was between 150-199 mg/dl and very high TG was defined when it was •500 mg/dl (NACEP, 2002).
Some previous studies showed that the most dramatic change in the lipid profile in normal pregnancy is serum hypertriglyceridemia, which may be as high as two to three folds in the third trimester over the levels in non pregnant women (Chiang et al., 1995). Triacylglycerol concentrations in the first trimester were similar to those of controls, there was a non-significant increase by the second trimester and by the third trimester the mean triacylglycerol concentration had doubled when compared with first and second trimester, they increase by about 200-300% in normal pregnancy (Martins et al., 1999). Rise in the serum triglycerides level is a major contributor in the pathogenesis of pre eclampsia. (Kashinakunti et al., 2010).
LOW-DENSITY LIPOPROTEIN (LDL)
Low density lipoprotein is one of the five major groups of lipoprotein that enable transport of lipid like cholesterol and triglyceriges within water-based bloodstream. They are commonly estimated to know how much low-density lipoprotein are driving progression of atherosclerosis. They are the primary carrier of plasma cholesterol, often referred to as bad cholesterol because it build up slowly in wall of arteries feeding the brain and heart. As a result of this form plague that clot the arteries causing artherosclerosis and increasing the risk of high blood pressure (Jackson, 1996).
During pregnancy, the LDL score increases dramatically in first trimester, second trimester and in the third trimester, its level peak at mid-third trimester, probably as a consequence of the hepatic effect of estradiol and progesterone (Desoye et al., 1987)). The change in triacylglycerols in normal pregnancy is important in relation to lipoprotein subclasses, such as LDL. These lipoproteins contain discrete subfractions of various sizes, densities and compositions, which differ in their ability to initiate atherogenesis (Rajman et al., 1994). For example, small, dense LDL particles do not bind readily to the LDL receptor and therefore remain in the circulation for longer. They also penetrate the arterial intima better than do larger ones and they are more readily oxidized, possibly because they contain less vitamin E and other antioxidants (Tribble et al., 1994). Finally, their uptake into macrophages to create foam cells, thus initiate atherogenesis. This may explain their identification as an independent risk factor for coronary heart disease.
HIGH-DENSITY LIPOPROTEIN (HDL)
Low density lipoprotein is also one of the five major groups of lipoprotein that enable transport of lipid like cholesterol and triglycerides within water-based bloodstream. In healthy individual, they are the smallest of all lipoprotein particles and are the densest because they contain highest portion of protein to cholesterol. About 30% of blood cholesterol is carried by HDL. It is considered to have anti-atherogenic properties since there is negative correlation between HDL and risk of cardiovascular disease, for HDL transport cholesterol from peripheral tissue to liver thereby reducing the amount of steroids in tissue and possibility of developing atherosclerotic plague and hence termed good cholesterol (Yakubu et al., 2008). High-density lipoprotein is considered normal when it is less than 40mg/dl and observed to be significantly higher in females than in males (syed et al., 2005).
Although not significant, in the first trimester of pregnancy, there is an increase in HDL but also slightly lower values of HDL in the second trimester was observed when compared with the first trimester of pregnancy especially between 22nd to 24th week of pregnancy. It increases during the third trimester when compared with the first trimester of pregnancy. HDL levels peaked specifically at approximately 28 weeks and remained unchanged till delivery (Idonije et al., 2011).
According to Takahashi et al., (2008) serum HDL levels increases only in pregnant patients with pre-eclampsia (PE) from the first to the second trimester, and that pregnant women that developed PE presented higher serum HDL and VLDL levels during the second trimester. Furthermore, there is also a possibly lowering effect of parity on HDL cholesterol (Stiphout et al., 1987). They are generally termed to be cardio-protective.
PATHOGENESIS OF CHANGE IN LIPID PROFILE DURING
PREGNANCY
Generally, serum lipids concentrations are affected by many factors such as environmental factors, alcohol intake, smoking, dietary intake and genetic factor (Zeyad et al., 2007). Lipid levels are mainly affected by maternal hormonal changes during pregnancy. Examples of such are insulin (which is observed to rise), progesterone, 17-β estradiol and Human Placental Lactogen. There are some evidences that progesterone which increases markedly in the second half of pregnancy may act to reset the lipostat in the hypothalamus (Mankuta et al., 2010). Also pregnancy is associated with hyperoestrogenaemia, and oestrogen is known to induce hepatic biosynthesis of endogenous triglycerides, which is carried by VLDL, this process may be modulated by hyperinsulinism found in pregnancy (Jayanta et al., 2006).
During pregnancy, there is an increase in the hepatic lipase activity and decrease in lipoprotein lipase activity. The hepatic lipase is responsible for the increased synthesis of the triglycerides at the hepatic level and the decreased activity of lipoprotein lipase is responsible for the decreased catabolism at the adipose tissue level. Due to the decrease in the activity of lipoprotein lipase, VLDL (Very Low-Density Lipoprotein) remains in the plasma for longer period which will therefore leads to the accumulation of LDL (Kashinakunti et al.,2010; Toescu et al,. 2004).
Outside pregnancy, it has also been found that smoking leads to increase in the concentration of serum total cholesterol, triglycerides, LDL-cholesterol, VLDL-cholesterol and fall in the levels of antiatherogenic HDL-cholesterol. Various mechanisms leading to lipid alteration by smoking are: nicotine stimulates sympathetic adrenal system leading to increased secretion of catecholamines resulting in increased lipolysis and increased concentration of plasma free fatty acids (FFA) which further result in increased secretion of hepatic free fatty acid and hepatic triglycerides along with VLDL- C in the blood stream. Fall in oestrogen levels occurs due to smoking which further leads to decreased HDL – cholesterol. Presence of hyperinsulinaemia in smokers leads to increased cholesterol, LDL-C, VLDL-C, and TG due to decreased activity of lipoprotein lipase (Neki, 2002).
Lipid profile is affected by diet, for example, soya protein has been observerd to reduce the concentrations of some atherogenic lipids in subjects with normal renal function (Shu-Tzu et al., 2006). Pregnancy and some disease state like celiac disease in which abnormal absorption of lipid occurs can also causes increase in lipid profile (Brar et al., 2006).
The major physiologic function of increase in the maternal lipid profile during pregnancy especially in the third trimester is in response to the maternal switch from carbohydrate to fat metabolism which is an alternative pathway for energy generation due to high energy demand (Idonije et al., 2011).
PATHOPHYSIOLOGY OF SERUM LIPID PROFILE
DURING PREGNANCY
As we have seen that there is a general increase in lipid profile during pregnancy, this elevation in lipid profile level except for HDL are associated with increased risk of atherosclerosis (Yakubu et al., 2008). Clinical studies have established that individuals with a small, dense LDL sub-fraction profile are more likely to develop coronary heart disease. These small dense LDL sub-fractions penetrate the arterial intima better than the larger ones and are more susceptible to oxidation than large, lighter ones and. Once they are oxidized, they will promote foam-cell formation and initiate endothelial dysfunction and thereby promote atherogenesis in a variety of ways (Martin et al., 1999).
Alteration in lipid profile is known to occur in diabetic pregnancy also, in which elevated triacylglyceride have been suggested as one of the causes (Kedari, 2010). The true influence of an altered lipid profile in the pathophysiology of pre- eclampsia (PE) has raised interest. PE is thus characterized by profound lipid changes similar to those found in atherosclerosis such as hypertriglyceridemia and relatively increased LDL level. There is also a positive correlation between serum triglycerides and the systolic blood pressure and diastolic blood pressure in pre eclampsia cases, therefore, rise in the serum triglycerides level has been suggested as a major contributor in the pathogenesis of pre-eclampsia (Kashinakunti et al., 2010).
Acne which is a common sign and symptom in pregnant women has been found relate with lipid profile. In acne patients, some abnormalities in lipid profile have been found. This abnormalities in lipid profile was suggested as one of the pathogenesis of acne (Zeyad et al.,2007).
Two consistent manifestations of altered maternal lipid metabolism associated with gestation are the accumulation of lipids in maternal tissues and the development of maternal hyperlipidaemia. Studies in recent past have incriminated abnormal lipid metabolism during pregnancy in the pathogenesis of ischaemic heart disease, intrauterine growth disease, intrauterine growth retardation, maternal obesity (Idonije et al., 2011). There is also an increased prevalence of angina, cholesterol gallstones, diabetes and obesity in post-menopausal women who have had several pregnancies (Martins et al., 1999).
It has been suggested that the increased lipid profile level especially that of triglycerides and LDL during pregnancy might be used to identify women who will develop atherogenic changes later in life.
PREVENTION/ TREATMENT
CONCLUSION/RECOMMENDATION
There is a general increase in lipid profile especially of total cholesterol (TC), triacylglycerol (TAG), low-density lipoprotein (LDL) but there are controversies on change in High-density lipoprotein (HDL) during pregnancy. These changes were suggested to be a risk factor for future atherosclerosis and cause further complication of some diseases like diabetes and pre-eclampsia that are associated with pregnancy.
Proper monitoring of diet should be advised for pregnant women Smoking should also be avoided during pregnancy
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