Is there any scripture that reveals why Woman with child born and unborn will be addected dreadfully in last day?
The Christians needed to flee (and ended up fleeing to Pella). When Jerusalem was surrounded by Roman armies, those Jews who had accepted Jesus - true Jews or Christians - remembered Jesus' words and fled when the Roman army temporarily withdrew. The non-believing Jews remained, and were destroyed when the Roman army returned. The believing women who were pregnant or breastfeeding were in a difficult position having to flee (worseso for the unbelievers, having to die). This difficult flight was the reason the Christians were to pray the flight wouldn't be in Winter or on the Sabbath. Note verse 34 says the generation Jesus was speaking to would not pass until all these things were fulfilled (and they were fulfilled in 70AD).
Matthew 24:15-34
When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand: )
Then let them which be in Judaea flee into the mountains:
Let him which is on the housetop not come down to take any thing out of his house:
Neither let him which is in the field return back to take his clothes.
And woe unto them that are with child, and to them that give suck in those days!
But pray ye that your flight be not in the winter, neither on the sabbath day:
For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be.
And except those days should be shortened, there should no flesh be saved: but for the elect's sake those days shall be shortened.
Then if any man shall say unto you, Lo, here is Christ, or there; believe it not.
For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect.
Behold, I have told you before.
Wherefore if they shall say unto you, Behold, he is in the desert; go not forth: behold, he is in the secret chambers; believe it not.
For as the lightning cometh out of the east, and shineth even unto the west; so shall also the coming of the Son of man be.
For wheresoever the carcase is, there will the eagles be gathered together.
Immediately after the tribulation of those days shall the sun be darkened, and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens shall be shaken:
And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory.
And he shall send his angels with a great sound of a trumpet, and they shall gather together his elect from the four winds, from one end of heaven to the other.
Now learn a parable of the fig tree; When his branch is yet tender, and putteth forth leaves, ye know that summer is nigh:
So likewise ye, when ye shall see all these things, know that it is near, even at the doors.
Verily I say unto you, This generation shall not pass, till all these things be fulfilled.