Kid­neys in preg­nancy

The im­pact of pre­gancy on re­nal dis­ease.

The Star Malaysia - Star2 - - HEALTH - by dR MIl­TOn lUM

THERE are many changes in the body dur­ing preg­nancy, and the kid­neys are no ex­cep­tion.

The blood flow to the kid­neys is in­creased by 50-70% in preg­nancy, with the most ob­vi­ous changes in the first two trimesters, i.e. up to 28 weeks of preg­nancy.

This re­sults in an in­crease in the glomeru­lar fil­tra­tion rate with re­sult­ing de­crease in blood lev­els of blood urea and cre­a­ti­nine, which are mark­ers of glomeru­lar func­tion.

So nor­mal lev­els of these two com­pounds dur­ing this pe­riod may in­di­cate re­nal dis­ease.

Blood pres­sure de­creases by about 10 mm Hg in the ini­tial 24 weeks of preg­nancy, and then grad­u­ally re­turns to pre-preg­nancy lev­els by 40 weeks.

As such, a blood pres­sure greater than 120/80 mm Hg may be a sign of the preg­nant woman’s pre­dis­po­si­tion to high blood pres­sure (hy­per­ten­sion).

There is also a change in the func­tion of the re­nal tubules, with in­creased loss of sugar into the urine (gly­co­suria), mak­ing the screen­ing of di­a­betes more prob­lem­atic.

The kid­neys in­crease in size by one to 1.5 cm in preg­nancy, and may stay that size for up to 12 weeks af­ter de­liv­ery.

The pelvis of the kid­neys and the ureters in­crease in size (di­late), pre­sum­ably un­der the ef­fects of pro­ges­terone pro­duced by the pla­centa.

This di­lata­tion is greater on the right, due to the ro­ta­tion of the uterus to the right and the di­lata­tion of the ovar­ian veins.

These changes may lead to col­lec­tions of urine (sta­sis), which in­creases the like­li­hood of uri­nary tract in­fec­tions.

In gen­eral, the func­tional changes in the uri­nary tract in preg­nancy reaches its max­i­mum ef­fects by the end of the sec­ond trimester, and then re­turn to the pre-preg­nancy lev­els.

The anatom­i­cal changes, how­ever, re­turn to pre-preg­nancy lev­els only up to three months af­ter de­liv­ery.

Uri­nary tract in­fec­tion

The di­lated col­lect­ing sys­tem of the uri­nary tract, uri­nary sta­sis and back­flow of urine from the blad­der into the ureters (vesi­coureteral re­flux) in preg­nancy in­creases the like­li­hood of bac­te­ria colonis­ing the urine (bac­teri­uria).

Preg­nant women with bac­teri­uria, but with no symp­toms, have an in­creased risk of uri­nary tract in­fec­tion (UTI), which can lead to an in­fec­tion of the kid­neys (pyelonephri­tis) in about onethird of those af­fected.

An­tibi­otic treat­ment of UTI has to be se­lec­tive as some an­tibi­otics can­not be pre­scribed in preg­nancy, e.g. trimetho­prim-sul­famethox­a­zole.

An acute in­fec­tion, or pyelonephri­tis, may have to be treated in hos­pi­tal with in­tra­venous an­tibi­otics and flu­ids.


Some pro­tein may be present in the urine in a nor­mal preg­nancy.

How­ever, amounts larger than 300mg per day are signs of pre­ex­ist­ing kid­ney dis­ease that has be­come worse, kid­ney dis­ease that oc­curred in preg­nancy, or the devel­op­ment of preg­nancy hy­per­ten­sion, es­pe­cially if it oc­curs af­ter 20 weeks of preg­nancy.

Acute re­nal fail­ure

Al­though rare, acute re­nal fail­ure does oc­cur in preg­nancy.

The causes may be sim­i­lar to those in non-preg­nant pa­tients, but there are spe­cific dis­or­ders of preg­nancy which can lead to acute re­nal fail­ure.

They in­clude ex­ces­sive and in­ad­e­quately treated vom­it­ing (hy­per­eme­sis gravi­darum), shock caused by bleed­ing from spon­ta­neous and/or sep­tic abor­tion, acute pyelonephri­tis, se­vere pre-eclamp­sia, eclamp­sia, HELLP (haemol­y­sis, el­e­vated liver en­zyme lev­els, low platelet count) syn­drome, uter­ine bleed­ing with sep­a­ra­tion of the pla­centa from the uterus (abrup­tio pla­cen­tae), se­vere post-par­tum haem­or­rhage, dis­sem­i­nated in­travas­cu­lar coag­u­la­tion and acute fatty liver of preg­nancy.

Other causes in­clude uri­nary tract stones and an­tiphos­pho­lipid syn­drome.

The man­age­ment of acute re­nal fail­ure in­cludes treat­ing the un­der­ly­ing cause and dial­y­sis.

Preg­nancy hy­per­ten­sion

High blood pres­sure (hy­per­ten­sion) is a com­mon com­pli­ca­tion of preg­nancy.

Preg­nancy hy­per­ten­sion is a sig­nif­i­cant cause of ma­ter­nal and foetal mor­bid­ity and mor­tal­ity.

Pre-eclamp­sia (PET) refers to hy­per­ten­sion and pro­tein­uria in women preg­nant for the first time (prim­i­gravida), whose blood pres­sure was pre­vi­ously nor­mal. It usu­ally oc­curs af­ter 32 weeks of preg­nancy, al­though it may oc­cur ear­lier.

PET re­solves within 10 days af­ter de­liv­ery of the baby. It oc­curs in prim­i­gravida and in older women who have had pre­vi­ous preg­nan­cies. PET is more likely to oc­cur in those with pre-ex­ist­ing hy­per­ten­sion, di­a­betes and in a twin preg­nancy.

Eclamp­sia refers to the oc­cur­rence of seizures in those with pre-eclamp­sia. Chronic hy­per­ten­sion oc­curs in women who have a prepreg­nancy blood pres­sure of 140/90 mm Hg or more prior to 20 weeks of preg­nancy. The like­li­hood of pre-eclamp­sia, abrup­tio pla­cen­tae, in­trauter­ine growth re­tar­da­tion and foetal death is in­creased in those with chronic hy­per­ten­sion.

Pre-eclamp­sia can also be su­per­im­posed on chronic hy­per­ten­sion. It oc­curs in women who have hy­per­ten­sion prior to 20 weeks of preg­nancy and de­velop a sud­den in­crease in blood pres­sure, pro­tein­uria and other bio­chem­i­cal ab­nor­mal­i­ties. It oc­curs more of­ten in older women or those who have some re­nal dis­ease.

As PET is re­solved with the de­liv­ery of the baby, a bal­ance has to be struck be­tween al­low­ing the foe­tus to ma­ture as much as pos­si­ble in­side the mother, and not com­pro­mis­ing on the mother’s safety.

Eclamp­sia and HELLP syn­drome are in­di­ca­tions for im­me­di­ate de­liv­ery, ir­re­spec­tive of the du­ra­tion of preg­nancy.

Cer­tain medicines used in the treat­ment of hy­per­ten­sion can­not be pre­scribed in preg­nancy.

Pre-ex­ist­ing kid­ney dis­ease

Women with kid­ney dis­ease can, and do, get preg­nant.

The im­pact on pa­tients with chronic re­nal dis­ease has to take into ac­count the ef­fects of preg­nancy on the kid­neys as stated ear­lier, and the ef­fects of kid­ney dis­ease on preg­nancy.

There is a de­te­ri­o­ra­tion of re­nal func­tion in some pa­tients with chronic re­nal dis­ease. The de­gree of dys­func­tion at the time of con­cep­tion, and the pres­ence and ex­tent of hy­per­ten­sion and pro­tein­uria, in­flu­ence the pa­tient’s out­come sig­nif­i­cantly.

Gen­er­ally, fer­til­ity is de­creased con­sid­er­ably in women with chronic re­nal dis­ease.

How­ever, some­times preg­nancy oc­curs even in women on dial­y­sis, but the risks of in­trauter­ine growth re­tar­da­tion, pre-term labour and foetal loss are in­creased, al­though foetal sur­vival rates are about 95% in most stud­ies.

The pro­gres­sion of the un­der­ly­ing ma­ter­nal kid­ney dis­ease is de­pen­dent on its sever­ity, rather than the spe­cific dis­ease.

Preg­nant women with di­a­betic nephropa­thy (kid­ney dis­ease) may de­velop wors­en­ing hy­per­ten­sion and pro­tein­uria.

Those with sys­temic lu­pus ery­the­mato­sus (SLE) may de­velop wors­en­ing hy­per­ten­sion and pro­tein­uria, which leads to prob­lems in dif­fer­en­ti­at­ing the cause of the prob­lem from PET.

The medicines that are usu­ally used in treat­ing SLE can­not be pre­scribed in early preg­nancy be­cause of the risk of caus­ing foetal ab­nor­mal­i­ties.

Trans­plan­ta­tion leads to a re­turn of fer­til­ity. Al­though most women with kid­ney trans­plants de­liver suc­cess­fully, there is an in­creased risk of spon­ta­neous abor­tion, ec­topic preg­nancy, preterm de­liv­ery, low birth­weight ba­bies, still­birth and neona­tal (ba­bies aged one month and be­low) death.

Other chal­lenges in­clude use of im­muno­sup­pres­sive medicines (drugs that lower the im­mune sys­tem), which in­crease the risk of hy­per­ten­sion and op­por­tunis­tic in­fec­tions (in­fec­tions that oc­cur be­cause the pa­tient has a weak im­mune sys­tem), some of which – e.g. cy­tomegalovirus and toxoplasma – poses risks to the foe­tus.

Women who de­velop kid­ney fail­ure in preg­nancy face more chal­lenges than non-preg­nant pa­tients.

Longer and more fre­quent dial­y­sis is as­so­ci­ated with bet­ter foetal out­comes.

The man­age­ment of preg­nan­cies in pa­tients with pre-ex­ist­ing re­nal dis­ease re­quires a team ap­proach in­volv­ing ob­ste­tri­cians, physi­cians, pae­di­a­tri­cians, nurses and other health care pro­fes­sion­als.

Pre-preg­nancy coun­selling and skilled ob­stet­ric man­age­ment have a ma­jor im­pact on the suc­cess of a preg­nancy or oth­er­wise.

Coun­selling helps in the se­lec­tion of an ap­pro­pri­ate time for preg­nancy; for ex­am­ple, when there is sta­bil­ity in the re­nal func­tion and good con­trol of the blood pres­sure.

It would be help­ful if there is dis­con­tin­u­a­tion or re­duc­tion in dosages of cer­tain medicines, e.g. steroids and im­muno­sup­pres­sives.

Mea­sures to re­duce the like­li­hood of in­fec­tions like rubella, hep­ati­tis B, toxoplasma and cy­tomegalovirus, among oth­ers, would also be help­ful.

The ma­jor cause of mor­bid­ity and mor­tal­ity in preg­nant pa­tients with re­nal dis­ease is preterm de­liv­ery.

As with PET. the chal­lenge for ob­ste­tri­cians is to strike the bal­ance be­tween al­low­ing the foe­tus to ma­ture as much as pos­si­ble, with­out com­pro­mis­ing on the mother’s safety. n Dr Mil­ton Lum is a mem­ber of the board of Med­i­cal De­fence Malaysia. This ar­ti­cle is not in­tended to re­place, dic­tate or de­fine eval­u­a­tion by a qual­i­fied doc­tor. The views expressed do not rep­re­sent that of any or­gan­i­sa­tion the writer is as­so­ci­ated with.

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