Quickening is about 15 weeks. So that gets you the first trimester you are arguing for.
From http://www.tnr.com/013100/easterbrook013100.html
From the twenty-second week to the twenty-fourth week, connections start to be established between the cortex and the thalamus, the part of the brain that translates thoughts into nervous-system commands. Fetal consciousness seems physically "impossible" before these connections form, says Fisk, of the Imperial College School of Medicine.
At about the twenty-third week the lungs become able to function, and, as a result, 23 weeks is the earliest date at which premature babies have survived. At 24 weeks the third trimester begins, and at about this time, as the cerebral cortex becomes "wired," fetal EEG readings begin to look more and more like those of a newborn. It may be a logical consequence, either of natural selection or of divine creation, that fetal higher brain activity begins at about the time when life outside the mother becomes possible. After all, without brain function, prematurely born fetuses would lack elementary survival skills, such as the ability to root for nourishment.
At about 26 weeks the cell structure of the fetal brain begins to resemble a newborn's, though many changes remain in store. By the twenty-seventh week, according to Dr. Phillip Pearl, a pediatric neurologist at Children's Hospital in Washington, D.C., the fetal EEG reading shows well-organized activity that partly overlaps with the brain activity of adults, although the patterns are far from mature and will continue to change for many weeks. By the thirty-second week, the fetal brain pattern is close to identical to that of a full-term baby.