Chronic TTTS occurs in 15% of MC twins and is responsible for 15-20% of perinatal death in twins. The patho-physiology involves chronic net shunting of blood from the donor to recipient twin. The donor becomes growth restricted, oliguric and develops anhydramnios ('stuck twin') and the recipient becomes polyuric with polyhy-dramnios and can go on to develop cardiac sequelae and hydrops. TTTS usually presents in the mid- but sometimes the third trimester, with gross discordance in amniotic fluid volume, with polyhydramnios in the recipient's and oligohydramnios in the donor's sac. The usual placental configuration comprises unbalanced deep artery to vein anastomoses with absent or inadequate compensation along superficial anastomoses . Thus Doppler detection of a compensatory artery-to-artery anastomosis antenatally substantially reduces the chance of developing TTTS, and where it does develop, predicts better prognosis [42,45].
Untreated, perinatal loss rates in the mid-trimester exceed 80%, with survivors at risk both of neurological morbidity acquired in utero or at birth and of cerebral palsy. Perinatal mortality rates have fallen to around 50% over the last decade due to a range of treatments comprising serial amnioreduction, septostomy, fetoscopic laser ablation of placental anastomoses (Plate 20.1, facing p. 562)
and cord occlusion. The recent randomized trial of endoscopic laser versus serial amnioreduction demonstrated that laser therapy as first line treatment was associated with better outcome, more pregnancies having at least one survivor to 6 months of age (76 versus 51%) along with fewer short-term neurological sequelae . These results are confirmed in a systematic view that included observational studies . Notwithstanding this, overall outcomes are far from perfect, in that two thirds of affected pregnancies still result in a dead or brain injured baby
. The current management dilemma concerns early stage disease , of which there were few patients in the randomized trial. Because TTTS resolves in 20-30% of stage I—II cases treated with a single amnioreduction, because perinatal survivals in the randomized amniore-duction/septostomy trial and the amnioreduction registry
 were empirically better than in the laser trial , and because laser could still be used in those that progress, there remains a role for test amnioreduction in early stage disease. This requires evaluation as amnioreduction may rarely lead to septal detachment, which can impede the technical success of a subsequent laser procedure.
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The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.