Influence of oligohydramnios on late pregnancy outcome

Abstract. Oligohydramnios of late pregnancy is an extremely important signal of a life threatening to the fetus ， which severely affect the prognosis of perinatal and makes perinatal mortality rate 5 times higher. [1].As one of the conditions that should be prevented in late pregnany， timely discovery and treatment of oligohydramnios can significantly reduce the perinatal mortality rate and improve the quality of perinatal [2] We will make a summary on the influence of oligohydramnios in late pregnancy outcome in this article.

Normally， amniotic fluid volume increases with the passes of gestational week and the volumes increases to about 800ml during late pregnancy to full-term pregnancy.We call it oligohydramnios when if the volume is less than 300ml.[3].

Key words： oligohydramnios late pregnancy ultrasonic diagnosis pregnancy outcome

1. The physiological functions of Amniotic fluid

Amniotic fluid can maintain a constant temperature （37.2 ～ 37.5 ℃）in amniotic cavity， providing the fetus with a suitable living conditions and activities space of with a constant temperature and pressure. It promotes the growth of fetal muscles and other tissues and organs and also prevent fetal malformation and limb adhesion； amniotic fluid can avoid fetal distress causing by uterine muscle wall or the direct fetal oppression to the umbilical cord； it can reduce the mechanical damage to the fetus from external violence impact and strong vibration， protecting the fetus； in addition the amniotic fluid can also keep a certain tension for the amniotic cavity， support the placenta atta to the uterine wall， thus preventing placental abruption； during pregnancy period， the amniotic fluid can reduce the pregnancy’s discomfort caused by the fetal movement； after rupture of membranes， amniotic fluid lubricates and washes the vagina， facilitates delivery， reduces the pain and harm to the maternal and fetus； there are some antibacterial substances， which plays a part in reducing infection.

2. Effect of oligohydramnios on perinatal infants

2.1 Effect on the fetus

Oligohydramnios in late pregnancy is usually companied with the placenta function decrease， which leads to the deficiency of utero-placental blood supply and a chornic oxygen deficiency of fetus in the urine. Amniotic fluid volume decreases as a result of fetal blood redistribution， majorly supplying the brain and the heart which causes renal blood flow decrease， leading to a reduction of the fetal urine-----main source of amniotic fluid[4]. A result of oligohydramnios is that the buffer effect reduces ，thus the uterus wraps the fetus body tightly. The movement of the fetus and uterus contraction makes the uterine wall close to the fetal with the intrauterine pressure directly affects the fetus. The umbilical cord compression or intrapartum contractions directly affect placental blood circulation ，leading to severe fetal hypoxia， and reflex caused by intestinal peristalsis of fetal hyperthyroidism， meconium row in the amniotic fluid of meconium-stained amniotic fluid at the same time， oligohydramnios can not dilute meconium， aggravating the degree of meconium-stained amniotic fluid. The less the amount of amniotic fluid meconium aspiration syndrome， fetal distress and neonatal asphyxia rate is higher， even worse， fetus dies in the uterine [5].

2.2 Effect on the neonatal

When fetal reserve force induces because of chronic hypoxia in the uterus neonatal effects of intrauterine， fetus has less tolerance to fetal hypoxia during delivery process， which easily leads to fetal distress. Neonatal asphyxia is result of fetal intrauterine hypoxia. Fetus with chronic fetal hypoxia often has lower birth weight or small gestational age [6]. After birth， there is a significant higher rate of getting neonatal disease， such as neonatal asphyxia， aspiration pneumonia，hypoxic-ischemic cerebral disease， Necrotizing Enterocolitis， renal dysfunction. More severe cases are cerebral palsy， or neonatal death. In addition， oligohydramnios results in a limitation of intrauterine fetal activity， causing fetal deformation or dislocation of shoulder joint， which commonly present as strephexopodia， strephenopodia （talipes equinus） and hip dislocation when it has given birth.[4].

3. Influence of oligohydramnios on the pregnancy

3.1 Oligohydramnios and pregnancy complications

Advanced oligohydramnios is often complicated with high risk pregnancy including prolonged pregnancy， premature rupture of membranes， intrauterine hypoxia， IUGR， low maternal blood volume， pregnancy-induced hypertension syndrome. As a result of oligohydramnios ，sensitivity of the uterus increases， postpartum pain becomes severer ， uterine contraction does not coordinate， and dilatation of cervix turns slower， leading to prolonged labour and postpartum hemorrhage rates increase，which has a significant effect on the Puerpera [5].Oligohydramnios is aggravated when combined with PIH myometrium，in which part of vasculars in Muscular layer and decidua of the uterine stenosis Irrigation and decidua part of or when pregnant women of low blood volume having Irrigation chorionic deficiency.Loss due to placental function of postterm pregnancy， the amnion and chorion lost normal dialysis， water and solute conversion disorder fetal-maternal formation of oligohydramnios [6]. More attention should be paid to pregnancy complications，which is high-risk pregnancy and intensifies the maternal and perinatal risk.

3.2 Oligohydramnios and mode of delivery

Oligohydramnios has a great effect on labor process and delivery. In the condition of oligohydramnios， the ability of can make the amniotic sac dilatation of the cervix weakens and the cervical dilatation slows down. Uterine wall will closely adhere to the body and contraction turns incoorperative， the force of it also decrease and lubrication of amniotic fluid to reduce road， fetal descent resistance increases， to extend the production process lead to fetal distress， meconium-stained amniotic fluid， neonatal asphyxia and neonatal morbidity increases， is also one of the important reasons to increase the operation rate of delivery. In operative delivery， the lack of amniotic fluid， vaginal dryness， and the uterine wall adhering to the fetus causes the operation difficult and laceration of birth canal， which includes complications such as soft birth canal laceration and uterus incision laceration in the delivery. Besides， there are short and long term complications with the increase ofcesarean section rate， and bring a series of cesarean section of， for instance the increasing the rate of postpartum hemorrhage and pelvic adhesion.

3.3 Influence of Oligohydramnios on the emotion of the pregnancy

Pregnant women diagnosed with oligohydramnios in perinatal examination are prone to be anxiety， fear [7].Maternal psychological factors are important factors that affect the delivery.If women in childbirth are in the anxiety and fear mental state， it is tend to cause a series of physiological and pathological reactions， including uterine atony， slower dilatation of cervix， pain sensitivity， prolonged labor and so on [8]； It also can make maternal neuroendocrine changes， sympathetic excitement， catecholamine release， leading to fetal intrauterine hypoxia， fetal distress and the rate of dystocia and cesarean section rate increase [9].Previous studies showed that [10]， maternal anxiety of the prgnant women also has a certain impact on neonatal weight and Apgar.To create a warm and comfortable environment， and giving psychological support in various forms is recommened.In addition，carrying out health education to pregnant women and their families， to answer questions in patients on with patience， informing the patients with oligohydramnios and by timely termination of pregnancy， shorten the birth process， amnioinfusion to minimize adverse effects on the fetus. Having pregnant women adapt and adjust of their psychological change and correctly recognize the discomfort in delivery process， reducing or eliminating anxiety， fear and labor stagnation caused by nerve[9].

4. The value of ultrasonography in diagnosing oligohydramnios

Oligohydramnios is the result of the destruction of the balance between the fetus and the placent，which has an adverse effects on perinatal outcomes [11]. With the development of perinatal medicine research， harm of oligohydramnios has also been recognized by general maternity workers and clinical palpation check method alone to diagnosis amniotic fluid volume has now been replaced [12]. The application of Ultrasonography，which is an important means of early detection of oligohydramnios ，has a high accuracy， and does no injury on pregnant women and fetuses in the diagnosis of oligohydramnios has a high value. In recent years， ultrasound is widely used in diagnosis of obstetrics and Gynecology diseases. It is reported [13] that ultrasound can be used in 27 aspects in the diagnosis of pregnant women. In a long time， people have always thought that the incidence rate of oligohydramnios is only 0.1%，however， with the application of ultrasound， patients with no signs and symptoms have been successively diagnosis as oligohydramnios， arresting the incidence rate to 0.5～4%[14]. As we can see， ultrasound scan plays an important role in the diagnosis of oligohydramnios.